Retinal FABP principally localizes to neurons and not to glial cells

The presence of fatty acid-binding protein (FABP) in the embryonic chick retina may be linked to the demand for polyunsaturated fatty acids in this developing neural tissue. There is a decline in the overall level of FABP as the retina matures, suggesting a role for FABP in cellular differentiation. However, this pattern is not present in the chick brain, indicating a unique function for FABP in the retina. Immunohistochemical staining of paraffin sections of chick retina from embryonic day 21 revealed immunopositive photoreceptor inner segments, outer nuclear layer, radial processes in the inner nuclear layer, a subpopulation of cells in the ganglion cell layer, and inner limiting membrane. This pattern suggested that FABP positive cells were photoreceptors, Müller (glial) cells, and possibly ganglion cells. Staining of sections for glutamine synthetase, an enzyme specific for Müller cells, was similar but not identical to the pattern observed with FABP; thus identification of these cells as FABP-positive was not conclusive. However, in retinal cells dissociated from day E14 embryos and cultured for one week, staining with FABP was more intense in the neurons than in the flat cells (presumed to be derived from the Müller cells). Retinal FABP thus appears to be localized predominantly in neurons, and may serve to sequester fatty acids in preparation for neurite outgrowth as the retinal cells differentiate.Abbreviations FABP Fatty Acid-Binding Protein - PUFA Polyunsaturated Fatty Acid     

Photoreactive fatty acid analogues that bind to the rat liver fatty-acid binding protein: 11-(5′-azido-salicylamido)-undecanoic acid derivatives

Summary Photoreactive probes for the hydrophobic pocket of the liver fatty acid-binding protein, 11-(5-azido-salicylamido)-undecanoic acid (5 ASU) and its acetyl ester (Ac5 ASU), were synthesized and their interaction with the protein was assessed. Fatty acid-binding proteins are closely related proteins which are abundantly expressed in tissues with active lipid metabolism. A simple model that assumes that the protein possesses a single kind of sites fitted the binding of radioiodinated 5 ASU to L-FABP satisfactorily. The apparent dissociation constant, 1.34×10^–7 M, evidenced a slightly higher affinity than that reported for C16–C20 fatty acids. Consistent with the binding curve, 5 ASU effectively competed with palmitic acid for the hydrophobic sites and the effect was nearly complete for concentrations of 1 gmM; oleic acid, in turn, displaced the radiolabelled probe. Irradiation at 366 nm of¹²⁵I-5 ASU bound to L-FABP caused the covalent cross-linking of the reagent. The amount of radioactivity covalently bound reached a maximum after 2 min thus agreeing with the photo-activation kinetics of the unlabelled compound that evidenced a t_1/2 of 31.1 sec. The yield with which probes bound to L-FABP became covalently linked to the protein, appraised after SDS-PAGE of irradiated samples, was estimated as 23 and 26 per cent for 5 ASU and Ac5 ASU respectively. In turn, irradiation of L-FABP incubated with 5ASU or Ac5 ASU resulted in the irreversible loss of about one fourth its ability to bind palmitic acid. Both results, taken together, suggested that the derivatives are linked to the protein through the sites for fatty acids. When cross-linking of¹²⁵I-5 ASU was performed after incubation with delipidated cytosol and products were analyzed by SDS-PAGE, a band was visualized in a position similar to that of purified L-FABP.Abbreviations FABP Fatty Acid-Binding Protein - L-FABP Hepatic FABP - I-FABP Intestinal FABP - C-FABP Cardiac FABP - 5 ASU-11 (5-azido-salicylamido)-undecanoic acid - Ac5 ASU-11 (O-acetyl-5-azido-salicylamido)-undecanoic acid     

Cellular binding proteins for fatty acids and retinoids: similar or specialized functions?

The cellular fatty acid-binding proteins (FABP) and cellular retinoid (retinol, retinoic acid)-binding proteins (CRtBP) are structurally and functionally-defined groups within an evolutionarily conserved gene family. CRtBP are expressed in both fully differentiated and developing tissues in a manner that supports a relationship to the action of retinoic acid in morphogenesis and cellular differentiation. The FABP are, by contrast, expressed only in fully differentiated tissues in a manner compatible with a major function in the metabolism of long-chain fatty acids (LCFA) for energy production or storage. The precise function(s) of FABP and CRtBP remain imperfectly understood, while subspecialization of function(s) within the two groups is suggested by the complex diversity in both of structurally distinct members that display striking tissue and temporal specificity of expression in addition to ligand specificity. Notwithstanding this considerable apparent functional diversity among the FABP and CRtBP, available evidence supports a dual set of generic functions for both protein groups in a) promoting cellular flux of poorly water-soluble ligands and their subsequent metabolic utilization or transformation, and b) sequestration of ligands in a manner that limits their association with alternative binding sites within the cell, of which members of the steroid hormone nuclear receptor superfamily (HNR) are a potentially important category. Theoretical as well as experimental models probing diffusional fluxes of LCFAin vitro and in living cells have provided support for a function for FABP in intracellular LCFA transport. Protein-bound ligand also appears to provide the substrate for metabolic transformation of retinoids bound to CRtBP, but convincing evidence is lacking for an analogous mechanism in the direct facilitation of fatty acid utilization by FABP. An emerging relationship between FABP and CRtBP function centers on their binding of, and induction by, ligands which activate or transform specific HNR-the retinoic acid receptors and the peroxisome proliferator activated receptor in the case of CRtBP and FABP, respectively. Evidence consistent with both a promotive role (provision of ligands for HNR) and a protective role (limiting availability of free ligand for HNR association) has been advanced for CRtBP. Available data supports a protective function for cellular retinoic acid-binding proteins (CRABP) and liver FABP (L-FABP) and points to the existence of ligand-defined, lipid-binding-protein-HNR relationships in which CRABP serve to attenuate the induction of gene expression by retinoic acid, and in which L-FABP may modulate a cellular adaptive multigene response to increased LCFA flux or compromised LCFA utilization. Furthermore, the emerging role of LCFA in the regulation of gene expression combined with the complex interplay between heterologous HNR-ligand associations and gene cross-regulation implies an important potential interaction between FABP, CRtBP, and their respective ligands in gene regulation.Abbreviations A-FABP Adipocyte Fatty Acid-Binding Protein - CRABP Cellular Retinoic Acid-Binding Protein(s) - CRABP I Cellular Retinoic Acid-Binding Protein type I - CRABP II Cellular Retinoic Acid-Binding Protein type II - CRBP Cellular Retinol-Binding Protein(s) - CRBP Cellular Retinol-Binding Protein typy I - CRBP II Cellular Retinol-Binding Protein type II - CRtBP Cellular Retinoid-Binding Proteins - FABP Fatty Acid-Binding Protein - H-FABP Heart Fatty Acid-Binding Protein - HNR steroid Hormone-type Nuclear Receptor - I-FABP Intestinal Fatty Acid-Binding Protein - LCFA Long-Chain Fatty Acids - L-FABP Liver Fatty Acid-Binding Protein - NBD-stearate 12-(N-methyl)-N-(7-nitrobenzo-2-oxa-1,3,-diazol-4-yl)amino)-octadecanoic acid - PPAR Peroxisome Proliferator-Activated Receptor - RAR Retinoic Acid Receptor(s) - RARE Retinoic Acid Response Element - RXR Retinoic acid X Receptors(s) - RXRE Retinoic acid X Response Element     

Release of heart fatty acid-binding protein into plasma after acute myocardial infarction in man

The release of cytoplasmic heart fatty acid-binding protein (H-FABP) into the plasma of cardiac patients up to 38 hr after the onset of the first clinical symptoms of acute myocardial infarction (AMI) was studied, using a sensitive direct and noncompetitive Enzyme Linked Immunosorbent Assay of the antigen capture type (sandwich ELISA), newly developed for the measurement of small amounts of human H-FABP in plasma samples. Plasma levels of H-FABP were compared with plasma activity levels of the myocardial cytoplasmic enzymes creatine kinase MB (CK-MB) and alpha-hydroxybutyrate dehydrogenase (-HBDH). Upper normal levels of H-FABP (19g/l), CK-MB (10 U/l) and -HBDH (160 U/l) as determined in plasma from 72 blood donors served as threshold levels. H-FABP levels were significantly elevated above their threshold level within 3 hr after AMI. Peak levels of H-FABP, CK-MB and -HBDH were reached 4.1 ± 0.9 hr, 8.4 ± 1.4 hr and 25.0 ± 9.5 hr (means ± S.D., n = 10) after acute myocardial infarction, respectively. Serial time curves of the plasma contents of H-FABP reveal that after myocardial infarction H-FABP is released in substantial amounts from human hearts. In 18 out of 22 patients with established AMI the plasma FABP level was at or above the threshold level in blood-samples taken within 3.5 hr after the first onset of symptoms of AMI, while for CK-MB this applied to 9 patients and for -HBDH to 6 patients. These findings suggest that for an early indication of acute myocardial infarction in man cytoplasmic heart fatty acid-binding protein is more suitable than heart type creatine kinase MB and/or alpha-hydroxybutyrate dehydrogenase. (Mol Cell Biochem116: 155–162,1992)Abbreviations H-FABP (cytoplasmic) Heart Fatty Acid-Binding Protein - LDH Lactate Dehydrogenase, -HBDH--Hydroxybutyrate Dehydrogenase - CK-MB Creatine Kinase-MB - AMI Acute Myocardial Infarction - PBS Phosphate Buffered Saline - BSA Bovine Serum Albumin     

Cellular fatty acid composition of six fastidious,gramnegative, xylem-limited bacteria from plants

Composition of cellular fatty acids was determined for strains of fastidious, Gramnegative, xylem-limited bacteria causing or associated with Pierce's disease of grapevine, phony disease of peach, plum leaf scorch, stunt of ragweed, elm leaf scorch, and periwinkle wilt. The most abundant fatty acids were straight-chain 150, 160, 170, and 180, unsaturated 161, 181, and unsaturated 17-and 19=carbon homologs. Minor fatty acids included straightchain 120, 140, 190, and 200; an unsaturated 15-carbon homolog; hydroxy-substituted 2-OH 120, 3-OH 120, and 3-OH 140; and branched chain iso-140 and iso-200. Cyclopropane acids were not detected. Physiological age had no effect on fatty acid composition. Class analysis of data indicated relative uniformity within the group. Saturated even-carbon chains comprised 31%–42%, unsaturated acids 41%–52%, saturated odd-carbon chains 10%–18%, hydroxysubstituted chains 2%–7%, and branched-chains 1%–4% of total fatty acids. The ratio of saturated-unsaturated acids ranged from 0.8 to 1.2.     

Assay of the binding of fatty acids by proteins: evaluation of the Lipidex 1000 procedure

Summary Fatty acid (FA) binding by fatty acid-binding protein (FABP) is frequently Monitored with the so-called Lipidex 1000 assay, in which protein associated and non-protein bound FA are separated by selectively binding the latter to Lipidex 1000. Careful evaluation of this assay showed that the use of aqueous FA solutions resulted in a Marked decrease (60 to 70%) of FA concentration due to their aspecific binding to the surface of the test-tube used. In addition, solutions of rat heart FABP in the Molar range also showed a concentration decrease up to 80% due to protein binding to the surface of the test-tube. Introduction of detergents, Triton X-100 or Tween 20, limited the FA loss to less than 20% and totally eliminated FABP adsorption. Kinetic parameters for the binding of [1-¹⁴C]oleic acid by purified rat heart FABP, assayed in the presence of Triton X-100, were found to be similar to those assayed in the absence of detergent, when adequate corrections were Made for losses of FA and FABP due to surface adsorption. Use of Tween 20 resulted in a substantial increase of the dissociation constant. The addition of 100 M Triton X-100 to the assay medium considerably facilitates the determination of kinetic parameters of fatty acid-binding by proteins.     

N-3 and n-6 fatty acid metabolism in undifferentiated and differentiated human intestine cell line (Caco-2)

Metabolism of n-6 and n-3 fatty acids in the undifferentiated and differentiated human adenocarcinoma colon cell line (Caco-2) was studied. In cells incubated with either 182n-6 or 183n-3, no significant amounts of long chain n-6 and n-3 metabolites were found. Incubation with either 183n-6 or 184n-3 raised significantly the levels of 203n-6 and 204n-3, respectively. In the undifferentiated cells, significant proportions of 203n-6 and 204n-3 were further 5-desaturated to form 204n-6 and 205n-3, respectively. Incubation with either 204n-6 or 205n-3 raised the levels of their direct elongation products, 224n-6 and 225n-3, respectively. Incubation with 224n-6 or 225n-3 increased the levels of 204n-6 and 205n-6. These results suggest that 6-desaturation in the Caco-2 cells is less active in comparision with elongation, 5-desaturation and retro-conversion. These enzymes were modulated by the state of differentiation, and appeared to be non-specific to n-3 and n-6 fatty acids. When cells were incubated with 183n-6 and 184n-3 concomitantly, the levels of incorporation of total n-6 fatty acids into cellular lipids were greater than those of the n-3 fatty acids, whereas the ratios of 20+22 carbon metabolites to 18-carbon precursor favored n-3 over n-6 fatty acids. These results suggest that n-3 and n-6 fatty acids were not metabolized identically in Caco-2 cells.     

Intracellular localization and domain organization of human TRIM41proteins

A human gene previously identified as a partial cDNA homologous to the gene of RET finger protein was characterized. Northern hybridization detected three messages of 3.3, 4.2, and 7.5kb. The coding sequences of the more abundant of the three messages, the 4.2 and the 3.3kb, were determined. The former encodes a 630 amino acid protein (TRIM41) and the latter a 518 amino acid protein (TRIM41). Green fluorescent protein (GFP) fusions of full-length TRIM41 and TRIM41 were both observed as speckles in the cytoplasm and the nucleus. The result was corroborated by Western analysis of cellular fractions. Results with GFP fusions of various segments of the TRIM41 proteins indicated that the nuclear transport of the proteins is mediated by an N-terminal segment common to both isoforms, but independent of a classical nuclear localization signal sequence.     

Comparison of fatty acids of marine fungi using multivariate statistical analysis

Summary Ten obligate marine fungi have as their principal fatty acids 160, 180, 181n9 and 182n6. The fatty acids ranged from 14 to 22 carbons, completely dominated by those with even numbers of carbons. The amount of unsaturated fatty acids varied between 35% and 80%. Each isolate contained small amounts of the acids 183n3 and 204n6. Branched, hydroxy- or cyclic fatty acids were not detected. Multivariate statistical, i.e. principal component analysis, showed that all ten strains could be distinguished on the basis of their fatty acid composition. These results indicate that the marine fungi do not have an unusual fatty acid composition and suggest that chemometric, multivariate analysis might be employed to confirm taxonomic relationships among these organisms.     

Mechanisms of regulation of liver fatty acid-binding protein

Liver fatty acid-binding protein (L-FABP) expression is modulated by developmental, hormonal, dietary, and pharmacological factors. The most pronounced induction is seen after treatment with peroxisome proliferators, which induce L-FABP coordinately with microsomal cytochrome P-450 4A1 and the enzymes of peroxisomal fatty acid -oxidation. These effects of peroxisome proliferators may be mediated by a receptor which has been shown to be activated by peroxisome proliferators in mammalian cell transfection studies. However, the peroxisome proliferators tested thus far do not bind to this receptor, known as the peroxisome proliferator-activated receptor (PPAR), and its endogenous ligand(s) also remain unknown. Peroxisome proliferators inhibit mitochondrial -oxidation, and one hypothesis is that the dicarboxylic fatty acid metabolites of accumulated LCFA, formed via the P-450 4A1 -oxidation pathway, serve as primary inducers of L-FABP and peroxisomal -oxidation. We have tested this hypothesis in primary hepatocyte cultures exposed to clofibrate (CF). Inhibition of P-450 4A1 markedly diminished, via a pre-translational mechanism, the CF induction of L-FABP and peroxisomal -oxidation. In further experiments, long-chain dicarboxylic acids, the final products of the P-450 4A1 -oxidation pathway, but not LCFA, induced L-FABP and peroxisomal -oxidation pre-translationally. These results suggest a role, in part, for long-chain dicarboxylic acids in mediating the peroxisome proliferator induction of L-FABP and peroxisomal -oxidation. We also found that LCFA, which undergo rapid hepatocellular metabolism, could become inducers of L-FABP and peroxisomal -oxidation under conditions where their metabolism was inhibited. The role of the PPAR in mediating these effects is unknown, but clearly warrants further study. The induction of L-FABP and peroxisomal -oxidation by LCFA and/or their -oxidized metabolites may provide a means for limiting the deleterious effects of increased intracellular concentrations of free LCFA, and thus act as an important hepatocellular adaptation to impairment or overload of mitochondrial LCFA oxidation.     

Cytosolic fatty acid binding proteins catalyze two distinct steps in intracellular transport of their ligands

Cytosolic long-chain fatty acid binding proteins (FABPs) are found in tissues that metabolize fatty acids. Like most lipid binding proteins, their specific functions remain unclear. Two classes have been described. Membrane-active FABPs interact directly with membranes during exchange of fatty acids between the protein binding site and the membrane, while membrane-inactive FABPs bind only to fatty acids that are already in aqueous solution. Despite these binding proteins, most fatty acids in cell cytoplasm appear to be bound to membranes. This paper reviews data suggesting that FABPs catalyze transfer of fatty acids between intracellular membranes, often across considerable intracellular distances. This process occurs in three distinct steps: dissociation of the fatty acid from a donor membrane, diffusion of the fatty acid across the intervening water layer, and binding to an acceptor membrane. Membrane-active FABPs catalyze dissociation of the fatty acid from the donor membrane and binding to the acceptor membrane, while membrane-inactive FABPs catalyze diffusion of fatty acids across the aqueous cytosol. Thus, FABPs catalyze all three steps in intracellular transport. A simple quantitative model has been developed that predicts the rate of intracellular transport as a function of the concentration, affinity and diffusional mobility of the binding protein. Different FABPs may have evolved to match the specific transport requirements of the cell type within which they are found.     

Solution structure of bovine heart fatty acid-binding protein (H-FABPc)

Fatty acid-binding protein (FABP) from bovine heart, a 15 kDa cytoplasmic protein has been investigated by multidimensional homonuclear and heteronuclear NMR-spectroscopy. Perdeuterated palmitic acid has been used as fatty acid ligand. The tertiary structure has been determined from distance geometry calculations with the variable target functions algorithm (DIANA) [1] utilizing 1027 interproton distance constraints, which were obtained from¹H-homo-nuclear NOESY spectra. Overlapping NOE crosspeaks were assigned by heteronuclear multidimensional NMR-experiments with a¹⁵N-labelled sample. The tertiary structure resembles a -barrel (-clam) consisting of ten anti-parallel -strands and a short helix-turn-helix motif. The -strands are arranged in two nearly orthogonal -sheets composed of 5 strands each. The solution structure is compared with the x-ray cyrstal structure of bovine heart [4] and rat intestinal FABPs.Abbreviations DOF-COSY Double Quantum Filtered Correlated Spectroscopy - TOCSY Total Correlated Spectroscopy - NOE Nuclear Overhauser Enhancement - NOESY Nuclear Overhauser Enhancement and Exchange Spectroscopy - HMQC Heteronuclear Multiple Quantum Coherence - FABP Fatty Acid-Binding Protein - FABP_c Cellular Fatty Acid-Binding Protein - H-FABP_c Cellular Heart Fatty Acid-Binding Protein - I-FABP_c Cellular Intestinal Fatty Acid-Binding Protein     

Homocysteine stimulates the expression of monocyte chemoattractant protein-1 in endothelial cells leading to enhanced monocyte chemotaxis

The effect of intraperitoneal administration of tocopherol (100 mg/kg wt/24 h) on ascorbate (0.4 mM) induced lipid peroxidation of mitochondria and microsomes isolated from rat liver and testis was studied. Special attention was paid to the changes produced on the highly polyunsaturated fatty acids C20:4 n6 and C22:6 n3 in liver and C20:4 n6 and C22:5 n6 in testis. The lipid peroxidation of liver mitochondria or microsomes produced a significant decrease of C20:4 n6 and C22:6 n3 in the control group, whereas changes in the fatty acid composition of the tocopherol treated group were not observed. The light emission was significantly higher in the control than in the tocopherol treated group. The lipid peroxidation of testis microsomes isolated from the tocopherol group produced a significant decrease of C20:4 n6 , C22:5 n6 and C22:6 n3, these changes were not observed in testis mitochondria. The light emission of both groups was similar. The treatment with tocopherol at the dose and times indicated showed a protector effect on the polyunsaturated fatty acids of liver mitochondria, microsomes and testis mitochondria, whereas those fatty acids situated in testis microsomes were not protected during non enzymatic ascorbateFe²⁺ lipid peroxidation. The protector effect observed by tocopherol treatment in the fatty acid composition of rat testis mitochondria but not in microsomes could be explained if we consider that the sum of C20:4 n6 + C22:5 n6 in testis microsomes is 2-fold than that present in mitochondria.     

Expression of fungal desaturase genes in cultured mammalian cells

Long-chain polyunsaturated fatty acids (LC-PUFA) are important components of cellular structure and function. Most of LC-PUFA are derived from linoleic acid and a-linolenic acid. In plants and fungi, these two acids can be synthesized from oleic acid via the action of two enzymes, 12 and 15-desaturases. Due to lack of these enzymatic activities and the ability to synthesize these two essential fatty acids, animals must obtain them from the diet. In this report, we demonstrated the expression of a fungal 12-desaturase gene in mouse L cells incubated in serum-free medium. The results showed a significant increase in the amount of linoleic acid with a concomitant decrease of oleic acid in cellular lipids. Most of the newly formed linoleic acid was incorporated into cellular phospholipids, particularly phosphatidylcholine. The increase of linoleic acid provided the substrate for the endogenous synthesis of (n-6) LC-PUFA, such as eicosadienoic acid (EDA), dihomo--linoleic acid (DGLA) and arachidonic acid (AA). Prolonged incubation further increased the levels of linoleic acid derived from oleic acid by the action of 12-desaturase, and the levels of 20:2n-6 produced from linoleic acid by the action of the endogenous elongase. However, prolonged incubation suppressed significantly the formation of DGLA and AA. In a separate study, a fungal 6-desaturase gene has also been expressed in the mouse L cells incubated in serum-containing medium. The result shows a significant increase in levels of 20:3n-6 and 20:4n-6. These findings demonstrate that through genetic modification, it is possible to (1) generate cell lines which no longer require dietary 'essential' fatty acids and (2) alter the endogenous fatty acid metabolism to enhance the production of LC-PUFA and their derivatives.     

Das Fettsäurespektrum des Flußkrebses Orconectes limosus und seine Beeinflussung durch die Nahrung

Zusammenfassung Das Fettsäurespektrum von männlichen Flußkrebsen Orconectes limosus wurde gaschromatographisch analysiert. Die Fettsäuren zeigen eine spezifische Verteilung auf die Lipidklassen. Das Gesamtspektrum entspricht dem Schema eines Süßwassertieres im Winter mit den größten Fraktionen: C160, C181, C202 und C204 (zusammen rund 53% der Gesamtfettsäuren). In verschiedenen Fraktionen wurden ungeradzahlige und verzweigte Fettsäuren gefunden.Durch Verfüttern von Kartoffeln und Lebertran kann das Spektrum beeinflußt werden. Die Fettsäuren in der Mitteldarmdrüse, und in weniger starkem Ausmaß im Restkörper, haben sich nach viermonatiger Fütterung mit Lebertran qualitativ und quantitativ dessen Spektrum angepaßt. Nach siebenmonatiger Fütterung mit Kartoffeln zeigen Mitteldarmdrüse und Restkörper ein Spektrum, das dem eines unbehandelten Kontrollkrebses ähnelt und sowohl C182 als auch höher ungesättigte Fettsäuren enthält. Hierfür kommen zwei Deutungen in Frage: Entweder wird das Spektrum der Fettsäuren in Strukturlipiden aufrechterhalten, oder es erfolgt de novo Synthese einer C18:2^6,9-Fettsäure und deren Verlängerung analog dem von Wirbeltieren bekannten Weg.

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The fatty acid composition in the crayfish, orconectes limosus, and the effect of nutrition

Summary The fatty acid composition in the male crayfish, Orconectes limosus, was analysed by gas-liquid chromatography. The fatty acids were found to have a specific distribution in different lipid classes. The composition corresponds to those of a fresh water animal in winter with the most important acids: C160, C181, C202, C204 (including about 53% of the total acids). In several lipid classes oddnumbered and branched chain fatty acids could be detected.Potatoe and fish-liver oil diets influence the fatty acid composition. After four months feeding with fish-liver oil the fatty acids in the hepatopancreas and to a lesser extent in the rest body show a similar spectrum as the fed oil. After feeding for seven months with potatoes hepatopancreas and rest body exhibit a fatty acid composition representative for the untreated animal, which contains C182 as well as higher unsaturated acids. These findings support the hypotheses that either the fatty acid composition in the structure lipids was maintained or that a C182^6,9-fatty acid was de novo synthesized and elongated analogous to the known vertebrate pathway.

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Herrn Prof. Dr. K. Urich bin ich für die Anregung zu der vorliegenden Arbeit und für die Durchsicht des Manuskriptes zu großem Dank verpflichtet.     

Molecular chaperones and protein folding in plants

Protein folding in vivo is mediated by an array of proteins that act either as foldases or molecular chaperones. Foldases include protein disulfide isomerase and peptidyl prolyl isomerase, which catalyze the rearrangement of disulfide bonds or isomerization of peptide bonds around Pro residues, respectively. Molecular chaperones are a diverse group of proteins, but they share the property that they bind substrate proteins that are in unstable, non-native structural states. The best understood chaperone systems are HSP70/DnaK and HSP60/GroE, but considerable data support a chaperone role for other proteins, including HSP100, HSP90, small HSPs and calnexin. Recent research indicates that many, if not all, cellular proteins interact with chaperones and/or foldases during their lifetime in the cell. Different chaperone and foldase systems are required for synthesis, targeting, maturation and degradation of proteins in all cellular compartments. Thus, these diverse proteins affect an exceptionally broad array of cellular processes required for both normal cell function and survival of stress conditions. This review summarizes our current understanding of how these proteins function in plants, with a major focus on those systems where the most detailed mechanistic data are available, or where features of the chaperone/foldase system or substrate proteins are unique to plants.     

Crystal structure of chicken liver basic fatty acid-binding protein at 2.7 Å resolution

The three-dimensional structure of chicken liver basic fatty acid-binding protein has been determined at 2.7 Å resolution by X-ray crystallography. Phases were calculated using the multiple isomorphous replacement procedure and a preliminary model was built. This model, with an initial R-factor of 0.57, was then improved by a cycle of refinement by simulated annealing which brought the R factor down to 0.32. The protein is structured as a compact 10-stranded--barrel which encapsulates a residual electron density that can be interpreted as a fatty acid molecule. The NH₂-terminus portion of the molecule contains two short -helices. The structure of this liver protein appears very similar to that of the Escherichia coli derived rat intestinal FABP recently determined by X-ray diffraction methods.     

Insights into binding of fatty acids by fatty acid binding proteins

Members of the phylogenetically related intracellular lipid binding protein (iLBP) are characterized by a highly conserved tertiary structure, but reveal distinct binding preferences with regard to ligand structure and conformation, when binding is assessed by the Lipidex method (removal of unbound ligand by hydrophobic polymer) or by isothermal titration calorimetry, a true equilibrium method. Subfamily proteins bind retinoids, subfamily II proteins bind bulky ligands, examples are intestinal bile acid binding protein (I-BABP) and liver fatty acid binding protein (L-FABP) which binds 2 ligand molecules, preferably monounsaturated and n-3 fatty acids. Subfamily III intestinal fatty acid binding protein (I-FABP) binds fatty acid in a bent conformation. The fatty acid bound by subfamily IV FABPs has a U-shaped conformation; here heart (H-) FABP preferably binds n-6, brain (B-) FABP n-3 fatty acids. The ADIFAB-method is a fluorescent test for fatty acid in equilibrium with iLBP and reveals some correlation of binding affinity to fatty acid solubility in the aqueous phase; these data are often at variance with those obtained by the other methods. Thus, in this review published binding data are critically discussed, taking into account on the one hand binding increments calculated for fatty acid double bonds on the basis of the solubility hypothesis, on the other hand the interpretation of calorimetric data on the basis of crystallographic and solution structures of iLBPs.     

Association of α-Dystrobrevin with Reorganizing Tight Junctions

Alpha-dystrobrevin (-DB) has been described primarily as a cytoplasmic component of the dystrophin-glycoprotein complex in skeletal muscle cells. Isoforms of -DB show different localization in cells and tissues; at basolateral membranes in epithelial cells, dystrobrevins mediate contact with the extracellular matrix, peripheral and transmembrane proteins and the filamentous actin cytoskeleton. Beside their structural role, -DBs are assumed to be important in cell signalling and cell differentiation. We have primarily assessed the role of -DB in two epithelial cell lines (MDCK I, HT 29), which represent different developmental stages and exhibit distinct permeability characteristics. Using a polyclonal anti--DB antibody, we have investigated its expression, localization and association with tight junction (TJ)- associated proteins (ZO-1, occludin) before and after protein kinase C (PKC) activation with phorbol myristate acetate. Distinct subsets of -DB isoforms were detected in the two cell lines by immunoblotting. In both cell lines there was submembranous localization of -DB both apically and basolaterally, shown with confocal imaging. PKC activation caused a reorganization of TJ, which was parallel to increased localization of -DB to TJ areas, most pronounced in MDCK I cells. Moreover, actin and ZO-1 co-immunoprecipitated with a-DB, as displayed with immunoblotting. Our findings suggest that a-dystrobrevin specifically is associated with the tight junctions during their reorganization.     

Gene expression, cellular localization, and enzymatic activity of diacylglycerol kinase isozymes in rat ovary and placenta

Female reproductive organs show remarkable cyclic changes in morphology and function in response to a combination of hormones. Evidence has accumulated suggesting that phosphoinositide turnover and the consequent diacylglycerol (DG) protein kinase C (PKC) pathway are intimately involved in these mechanisms. The present study has been performed to investigate the gene expression, cellular localization, and enzymatic activity of the DG kinase (DGK) isozymes that control the DG-PKC pathway. Gene expression for DGK, -, -, and - was detected in the ovary and placenta. Intense expression signals for DGK and - were observed in the theca cells and moderate signals in the interstitium and corpora lutea of the ovary. On the other hand, signals for DGK were seen more intensely in granulosa cells. In the placenta, signals for DGK and - were observed in the junctional zone, whereas those for DGK were detected in the labyrinthine zone. At higher magnification, the signals for DGK were mainly discerned in giant cytotrophoblasts, and those for DGK were found in small cytotrophoblasts of the junctional zone. DGK signals were observed in all cellular components of the labyrinthine zone, including mesenchyme, trabecular trophoblasts, and cytotrophoblasts. DGK signals were detected in the junctional zone on day 13 and 15 of pregnancy and were diffusely distributed both in the labyrinthine and junctional zones at later stages. The present study reveals distinct patterns of mRNA localization for DGK isozymes in the rat ovary and placenta, suggesting that each isozyme plays a unique role in distinct cell types in these organs.This work was supported by Grants-in-Aids from the Ministry of Education, Culture, Sports, Science, and Technology (MEXT) of Japan, the Uehara Memorial Foundation, the ONO Medical Research Foundation, the Ciba-Geigy Foundation (Japan) for the Promotion of Science, the Kato Memorial Bioscience Foundation, and the Yamagata Health Support Foundation (to K.G.).