A single lysyl residue defines the binding specificity of a human odorant-binding protein for aldehydes

Odorant-binding proteins (OBPs) are small abundant soluble proteins belonging to the lipocalin superfamily, which are thought to carry hydrophobic odorants through aqueous mucus towards olfactory receptors. Human variant hOBP-2A has been demonstrated to bind numerous odorants of different chemical classes with a higher affinity for aldehydes and fatty acids. Three lysyl residues of the binding pocket (Lys62, Lys82 and Lys112) have been suggested as candidates for playing such a role. Here, using site-directed mutagenesis and fluorescent probe displacements, we show that Lys112 is the major determinant for governing hOBP-2A specificity towards aldehydes and small carboxylic acids.     

A retrospective study of the microbiological and parasitological status of laboratory rodents in France

Between 1988 and 1997, 72 mouse colonies and 38 rat colonies were examined for the presence of bacteria parasite infections. Among mouse and rat bacteria, high positive rates were observed with Proteus species (sp.), Pasteurella pneumotropica, Mycoplasma sp. and Pseudomonas aeruginosa. Concerning murine colonies, parasites frequently detected were Tritrichomonas sp., Syphacia sp., Aspiculuris tetraptera, Entamoeba muris, Spironucleus muris, Myobia musculi, Chilomastix sp. and Myocoptes musculinus. In rats, high rates were obtained with Syphacia sp., Tritrichomonas sp., Spironucleus muris, Entamoeba muris and Chilomastix sp. During the first part of the last decade, some agents such as Clostridium piliforme, Citrobacter sp., Mycoplasma sp., Pseudomonas aeruginosa, Myobia musculi, Radfordia ensifera, Spironucleus muris and Giardia muris were often found among rodents, and most of them were still present in 1997. At the time of our study, results point out that some agents are still persistent, even increasing during the same period. It is particularly the case for parasites such as Entamoeba muris and the oxyurids, but also for bacteria like Proteus sp. and Klebsiella pneumoniae. We can thus conclude that only very limited success has been achieved in preventing microbial and parasitic infections in mice and rats colonies.     

Identification of germline genomic copy number variation in familial pancreatic cancer

Adenocarcinoma of the pancreas is a significant cause of cancer mortality, and up to 10?% of cases appear to be familial. Heritable genomic copy number variants (CNVs) can modulate gene expression and predispose to disease. Here, we identify candidate predisposition genes for familial pancreatic cancer (FPC) by analyzing germline losses or gains present in one or more high-risk patients and absent in a large control group. A total of 120 FPC cases and 1,194 controls were genotyped on the Affymetrix 500K array, and 36 cases and 2,357 controls were genotyped on the Affymetrix 6.0 array. Detection of CNVs was performed by multiple computational algorithms and partially validated by quantitative PCR. We found no significant difference in the germline CNV profiles of cases and controls. A total of 93 non-redundant FPC-specific CNVs (53 losses and 40 gains) were identified in 50 cases, each CNV present in a single individual. FPC-specific CNVs overlapped the coding region of 88 RefSeq genes. Several of these genes have been reported to be differentially expressed and/or affected by copy number alterations in pancreatic adenocarcinoma. Further investigation in high-risk subjects may elucidate the role of one or more of these genes in genetic predisposition to pancreatic cancer.     

Difference in lipid packing sensitivity of exchangeable apolipoproteins apoA-I and apoA-II: an important determinant for their distinctive role in lipid metabolism

Exchangeable apolipoproteins A-I and A-II play distinct roles in reverse cholesterol transport. ApoA-I interacts with phospholipids and cholesterol of the cell membrane to make high density lipoprotein particles whereas apolipoprotein A-II interacts with high density lipoprotein particles to release apolipoprotein A-I. The two proteins show a high activity at the aqueous solution/lipid interface and are characterized by a high content of amphipathic α-helices built upon repetition of the same structural motif. We set out to investigate to what extent the number of α-helix repeats of this structural motif modulates the affinity of the protein for lipids and the sensitivity to lipid packing. To this aim we have compared the insertion of apolipoproteins A-I and A-II in phospholipid monolayers formed on a Langmuir trough in conditions where lipid packing, surface pressure and charge were controlled. We also used atomic force microscopy to obtain high resolution topographic images of the surface at a resolution of several nanometers and performed statistical image analysis to calculate the spatial distribution and geometrical shape of apolipoproteins A-I and A-II clusters. Our data indicate that apolipoprotein A-I is sensitive to packing of zwitterionic lipids but insensitive to the packing of negatively charged lipids. Interestingly, apolipoprotein A-II proved to be insensitive to the packing of zwitterionic lipids. The different sensitivity to lipid packing provides clues as to why apolipoprotein A-II barely forms nascent high density lipoprotein particles while apolipoprotein A-I promotes their formation. We conclude that the different interfacial behaviors of apolipoprotein A-I and apolipoprotein A-II in lipidic monolayers are important determinants of their distinctive roles in lipid metabolism.     

Methionine sulfoxide reductases preferentially reduce unfolded oxidized proteins and protect cells from oxidative protein unfolding

Reduction of methionine sulfoxide (MetO) residues in proteins is catalyzed by methionine sulfoxide reductases A (MSRA) and B (MSRB), which act in a stereospecific manner. Catalytic properties of these enzymes were previously established mostly using low molecular weight MetO-containing compounds, whereas little is known about the catalysis of MetO reduction in proteins, the physiological substrates of MSRA and MSRB. In this work we exploited an NADPH-dependent thioredoxin system and determined the kinetic parameters of yeast MSRA and MSRB using three different MetO-containing proteins. Both enzymes showed Michaelis-Menten kinetics with the K(m) lower for protein than for small MetO-containing substrates. MSRA reduced both oxidized proteins and low molecular weight MetO-containing compounds with similar catalytic efficiencies, whereas MSRB was specialized for the reduction of MetO in proteins. Using oxidized glutathione S-transferase as a model substrate, we showed that both MSR types were more efficient in reducing MetO in unfolded than in folded proteins and that their activities increased with the unfolding state. Biochemical quantification and identification of MetO reduced in the substrates by mass spectrometry revealed that the increased activity was due to better access to oxidized MetO in unfolded proteins; it also showed that MSRA was intrinsically more active with unfolded proteins regardless of MetO availability. Moreover, MSRs most efficiently protected cells from oxidative stress that was accompanied by protein unfolding. Overall, this study indicates that MSRs serve a critical function in the folding process by repairing oxidatively damaged nascent polypeptides and unfolded proteins.     

Comparative study of serine-plasmalogens in human retina and optic nerve: identification of atypical species with odd carbon chains

The objective of this work was to detect and identify phosphatidylserine plasmalogen species in human ocular neurons represented by the retina and the optic nerve. Plasmalogens (vinyl-ether bearing phospholipids) are commonly found in the forms of phosphatidylcholine and phosphatidylethanolamine in numerous mammalian cell types, including the retina. Although their biological functions are unclear, the alteration of cellular plasmalogen content has been associated with several human disorders such as rhizomelic chondrodysplasia punctata Type 2 and primary open-angle glaucoma. By using liquid chromatography coupled to high-resolution and tandem mass spectrometry, we have identified for the first time several species of phosphatidylserine plasmalogens, including atypical forms having moieties with odd numbers of carbons and unsaturation in sn-2 position. Structural elucidation of the potential phosphatidylserine ether linked species was pursued by performing MS(3) experiments, and three fragments are proposed as marker ions to deduce which fatty acid is linked as ether or ester on the glycerol backbone. Interpretation of the fragmentation patterns based on this scheme enabled the assignment of structures to the m/z values, thereby identifying the phosphatidylserine plasmalogens.     

Occurrence, biosynthesis and functions of N-acylphosphatidylethanolamines (NAPE): not just precursors of N-acylethanolamines (NAE)

N-acylphosphatidylethanolamine (NAPE) is a minor phospholipid resulting from the transfer of an acyl chain from an acyl donor to the primary amine of the ethanolamine moiety of phosphatidylethanolamine (PE). Occurring in plant and animal kingdoms as well as in prokaryotic cells, it is synthesized in higher amounts in membranes during cellular stresses and tissue damage, and it is widely thought to be the precursor of the lipid mediator, N-acylethanolamine (NAE), which modulates the endocannabinoid signaling pathway and therefore regulates various physiological processes. However, recent studies have shown that NAPE is also a bioactive molecule that is involved in several physiological functions. The present paper reviews the occurrence of NAPE in animals and plants and focuses on the various properties of NAPE observed in vitro and in vivo. The different metabolic pathways promoting the synthesis and degradation of NAPE are also discussed and the differences between animals and plants are underlined.     

Modulation of the multilamellar membrane organization and of the chiral macrodomains in the diatom Phaeodactylum tricornutum revealed by small-angle neutron scattering and circular dichroism spectroscopy

Diatoms possess effective photoprotection mechanisms, which may involve reorganizations in the photosynthetic machinery. We have shown earlier, by using circular dichroism (CD) spectroscopy, that in Phaeodactylum tricornutum the pigment-protein complexes are arranged into chiral macrodomains, which have been proposed to be associated with the multilamellar organization of the thylakoid membranes and shown to be capable of undergoing light-induced reversible reorganizations (Szabó et al. Photosynth Res 95:237, 2008). Recently, by using small-angle neutron scattering (SANS) on the same algal cells we have determined the repeat distances and revealed reversible light-induced reorganizations in the lamellar order of thylakoids (Nagy et al. Biochem J 436:225, 2011). In this study, we show that in moderately heat-treated samples, the weakening of the lamellar order is accompanied by the diminishment of the psi-type CD signal associated with the long-range chiral order of the chromophores (psi, polymer or salt-induced). Further, we show that the light-induced reversible increase in the psi-type CD is associated with swelling in the membrane system, with magnitudes larger in high light than in low light. In contrast, shrinkage of the membrane system, induced by sorbitol, brings about a decrease in the psi-type CD signal; this shrinkage also diminishes the non-photochemical quenching capability of the cells. These data shed light on the origin of the psi-type CD signal, and confirm that both CD spectroscopy and SANS provide valuable information on the macro-organization of the thylakoid membranes and their dynamic properties; these parameters are evidently of interest with regard to the photoprotection in whole algal cells.     

Voltage-dependent-anion-channels (VDACs) in Arabidopsis have a dual localization in the cell but show a distinct role in mitochondria

In mammals, the Voltage-dependent anion channels (VDACs) are predominant proteins of the outer mitochondrial membrane (OMM) where they contribute to the exchange of small metabolites essential for respiration. They were shown to be as well associated with the plasma membrane (PM) and act as redox enzyme or are involved in ATP release for example. In Arabidopsis, we show that four out of six genomic sequences encode AtVDAC proteins. All four AtVDACs are ubiquitously expressed in the plant but each of them displays a specific expression pattern in root cell types. Using two complementary approaches, we demonstrate conclusively that the four expressed AtVDACs are targeted to both mitochondria and plasma membrane but in differential abundance, AtVDAC3 being the most abundant in PM, and conversely, AtVDAC4 almost exclusively associated with mitochondria. These are the first plant proteins to be shown to reside in both these two membranes. To investigate a putative function of AtVDACs, we analyzed T-DNA insertion lines in each of the corresponding genes. Knock-out mutants for AtVDAC1, AtVDAC2 and AtVDAC4 present slow growth, reduced fertility and yellow spots in leaves when atvdac3 does not show any visible difference compared to wildtype plants. Analyses of atvdac1 and atvdac4 reveal that yellow areas correspond to necrosis and the mitochondria are swollen in these two mutants. All these results suggest that, in spite of a localization in plasma membrane for three of them, AtVDAC1, AtVDAC2 and AtVDAC4 have a main function in mitochondria.