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1.
Summary In stressed rats the tanycytes of the ventrolateral wall of the third ventricle exhibit by light microscopic immunohistochemistry a positive staining for neurohormones which is distinctly limited to the distal perivascular end of the tanycyte process. Since by electron microscopic immuncytochemistry the tanycyte cytoplasm does not show any reaction product, the light microscopic reaction most likely results from a labeling of the intercellular space in the direct vicinity of the subendothelial cleft. Whether this subendothelial space is permeable to neurohormones was tested by injection of HRP1. In the region of the arcuate nucleus 30 min after intravenous application, the marker is affixed to the membranes of the perivascular tanycyte processes in the subendothelial cleft of capillaries possessing non-fenestrated endothelia. Occasionally, HRP penetrates for a short distance between the tanycytes. Then the labeling of the intercellular cleft ends abruptly. Here, several parallel ridges of tight junctions between the perivascular distal tanycyte processes are found by the freezeetching technique. Since HRP cannot reach the subendothelial clefts of this region by passing through capillary walls due to the presence of a blood-brain barrier, it is suggested that the marker penetrates from the median eminence this far via the subendothelial extracellular space. It is prevented from spreading further by the tight junctions of the perivascular tanycyte endings. The same way may be taken by the neurohormones. Hence, a border area exists adjacent to the dorsolateral aspect of the neurohemal region of the median eminence where the tanycytes isolate the neuropil from the cerebrospinal fluid not only by their apical tight junctions, but also by basal tight junctions from the subendothelial cleft. This communicates with the perivascular space of the portal vessels.Supported by the Deutsche Forschungsgemeinschaft (Grant Nr. Kr. 569/2) and Stiftung VolkswagenwerkDedicated to Professor Dr. R. Ortmann on the occasion of his 65th birthday.The skilful technical assistance of Miss K. Bielenberg, Mrs. A. Hinz and Mrs. H. Prien is thankfully acknowledged 相似文献
2.
It is now generally accepted that the intercellular cleft between adjacent endothelial cells is the primary pathway for the transluminal movement of water and small ions in the vasculature. A steady-state theoretical model has been developed to show quantitatively how the geometry of the intercellular cleft between adjacent endothelial cells is related to both the water movement and pressure distribution in the subendothelial space and to examine how the existence of a subendothelial interaction layer affects the hydraulic resistance of the media of vessels of varying wall thickness. The velocity and pressure fields in the media are described using porous matrix theory based on Darcy's law and a lubrication-type analysis is used to describe the flow in a variable geometry intercellular cleft. These two equations are solved simultaneously to determine the unknown pressure distribution beneath the endothelium and the flow in the arterial media. Application of this model shows that, when the tight junction in the cleft is 26 A or less, more than half of the total hydraulic resistance of the wall occurs across the endothelial cell monolayer, for a vessel whose wall thickness is less than 0.02 cm. This finding is in good agreement with the experimental findings of Vargas, et al. (1978) for rabbit aorta. Contrary to previous belief, the model shows that the filtration resistance of an arterial wall with intact endothelium does not scale linearly with wall thickness due to the highly nonlinear resistance of the endothelial interaction layer. 相似文献
3.
In an effort to understand the molecular basis of chronic beryllium disease (CBD), a study of the chemical relationship between beryllium, antigen, and the major histocompatibility complex II, HLA-DP, was undertaken. A homology model of the HLA-DP protein was developed. An analysis of the sequences of HLA-DPB1 and HLA-DPA1 alleles most common among CBD patients revealed several carboxylate rich regions in the peptide-binding cleft. These regions contain many hard Lewis base sites that may provide bonding opportunities for beryllium, a hard Lewis acid. Quantum chemistry calculations and structural database results support the presence of beryllium clusters, bridged by carboxylate, hydroxo, and/or oxo ligands, in the HLA-DP binding cleft. These results strongly suggest that beryllium clusters are an integral part of the antigen, and may even act solely as antigen. This work provides an initial model for thinking about beryllium interactions with proteins relevant to CBD and other metal-induced diseases. 相似文献
4.
Olgac U Knight J Poulikakos D Saur SC Alkadhi H Desbiolles LM Cattin PC Kurtcuoglu V 《Journal of biomechanics》2011,44(13):2466-2471
Subendothelial accumulation of low-density lipoprotein (LDL) in arterial walls is an initiator of atherosclerotic plaque formation. We report here on the correlation between healthy state subendothelial LDL concentration distribution and sites of subsequent plaque formation in coronary arteries of patients with coronary artery disease (CAD). We acquired left (LCA) and right coronary artery (RCA) and atherosclerotic plaque geometries of 60 patients with CAD using dual-source computed tomography angiography. After virtually removing all plaques to obtain an approximation of the arteries' healthy state, we calculated LDL concentration in the artery walls as a function of local lumen-side shear stress. We found that maximum subendothelial LDL concentrations at plaque locations were, on average, 45% (RCA) and 187% (LCA) higher than the respective average subendothelial concentration. Our results demonstrate that locally elevated subendothelial LDL concentration correlates with subsequent plaque formation at the same location. 相似文献
5.
Le Roy K Verhaest M Rabijns A Clerens S Van Laere A Van den Ende W 《The New phytologist》2007,176(2):317-324
Recently, the three-dimensional structure of chicory (Cichorium intybus) fructan 1-exohydrolase (1-FEH IIa) in complex with its preferential substrate, 1-kestose, was determined. Unfortunately, no such data could be generated with high degree of polymerization (DP) inulin, despite several soaking and cocrystallization attempts. Here, site-directed mutagenesis data are presented, supporting the presence of an inulin-binding cleft between the N- and C-terminal domains of 1-FEH IIa. In general, enzymes that are unable to degrade high DP inulins contain an N-glycosylation site probably blocking the cleft. By contrast, inulin-degrading enzymes have an open cleft configuration. An 1-FEH IIa P294N mutant, introducing an N-glycosylation site near the cleft, showed highly decreased activity against higher DP inulin. The introduction of a glycosyl chain most probably blocks the cleft and prevents inulin binding and degradation. Besides cell wall invertases, fructan 6-exohydrolases (6-FEHs) also contain a glycosyl chain most probably blocking the cleft. Removal of this glycosyl chain by site-directed mutagenesis in Arabidopsis thaliana cell wall invertase 1 and Beta vulgaris 6-FEH resulted in a strong decrease of enzymatic activities of the mutant proteins. By analogy, glycosylation of 1-FEH IIa affected overall enzyme activity. These data strongly suggest that the presence or absence of a glycosyl chain in the cleft is important for the enzyme's stability and optimal conformation. 相似文献
6.
Morstadt L Bohm A Yüksel D Kumar K Stollar BD Baleja JD 《Protein science : a publication of the Protein Society》2008,17(3):458-465
The surrogate light chain (SLC) is a key regulator of B cell development in the bone marrow, resulting in mature B cells that produce antibodies that are capable of interacting with antigens. The SLC comprises two noncovalently interacting proteins: VpreB and 14.1. We engineered a construct to represent the complete immunoglobulin-like domain of the SLC variable domain in a single protein chain that could be bacterially expressed. In this construct, the incomplete immunoglobulin domain of VpreB (residues 1-102) was linked to the J-segment of 14.1 (residues 40-53), which provided one beta-strand to complete the V-like domain (VpreBJ). Because VpreBJ has the interface to VH chains, but lacks the unique region of 14.1, which is important for SLC signaling, we predict that a properly folded VpreBJ would have the potential to act as a dominant negative mutant of the surrogate light chain. X-ray crystallography of VpreBJ at 2.0 A resolution showed that the engineering was successful. With its two beta-pleated sheets, packed face-to-face, the single chain VpreBJ resembles a mature light chain immunoglobulin V-domain (VL). The surface that would normally interact with the VH chain interacts with a crystallographically related VpreBJ molecule. The presence of dimeric species in solution was verified by analytical ultracentrifugation. VpreBJ is easily overexpressed in bacteria, while retaining the native conformation of an immunoglobulin domain, and thus may serve as an important reagent for future studies in B-cell development. 相似文献
7.
Brown MD Jin L Jien ML Matsumoto AH Helm GA Lusis AJ Frank JS Shi W 《Journal of lipid research》2004,45(6):1155-1161
LDL deposition in the subendothelium of arterial walls is the initial event in the development of atherosclerosis. The deposited LDL undergoes oxidative modification by arterial wall cells to become oxidized LDL and consequently contributes to atherosclerotic formation. Using mouse strains C57BL/6J (B6) and C3H/HeJ (C3H), which differ markedly in susceptibility to atherosclerosis, we determined whether variation in subendothelial retention of apolipoprotein B (apoB)-containing lipoproteins constitutes a genetic component in atherosclerosis. Lipoprotein retention was quantitated by Western blot analysis to detect the presence of apoB in aortic walls before foam cells developed. In both dietary and apoE-deficient models, B6 mice exhibited up to a 2-fold increase of apoB in the aortic wall compared with C3H mice. This increase could not be attributed to differences in plasma lipid levels of the two strains. In vitro, endothelial cells from C3H mice took up more acetylated and oxidized LDL but not native LDL and converted more native LDL to oxidized LDL than did endothelial cells from B6 mice. C3H mice expressed more scavenger receptor A in their aortic wall than B6 mice. Thus, variation in the subendothelial retention of apoB-containing lipoproteins cannot explain the dramatic difference in atherosclerosis susceptibility between B6 and C3H mice, and endothelial cells may play a role in alleviating lipid accumulation in arterial walls. 相似文献
8.
Structural and biosynthetic studies on linkage region between poly(galactosylglycerol phosphate) and peptidoglycan in Bacillus coagulans 总被引:3,自引:0,他引:3
S Kaya K Yokoyama Y Araki E Ito 《Biochemical and biophysical research communications》1983,111(1):312-318
The HF treatment of teichoic acid-glycopeptide complexes isolated from lysozyme digests of Bacillus coagulans AHU 1366 cell walls gave a disaccharide, glucosyl beta (1 leads to 4)N-acetylglucosamine, along with dephosphorylated repeating units of the teichoic acid chain, galactosyl alpha (1 leads to 2) glycerol. Mild alkali treatment of the complexes yielded the disaccharide linked to glycopeptide, whereas direct heating of the cell walls at pH 2.5 yielded the same disaccharide linked to teichoic acid. The Smith degradation of the complexes revealed that the galactose residue is a component of backbone chain. Thus it is concluded that this disaccharide is involved in the linkage region between poly(galactosylglycerol phosphate) and peptidoglycan in cell walls. Membrane-catalyzed synthesis of this disaccharide on a lipid followed by transfer of glycerol phosphate from CDP-glycerol to the disaccharide-linked lipid in the absence or in the presence of UDP-galactose also supports this conclusion. 相似文献
9.
Todd L. Sladek 《Journal of theoretical biology》1986,120(4):457-465
Mycoplasmas are wall-less prokaryotes which have small genomes and are known to have evolved from ancestors of Gram-positive bacteria. A model is proposed to explain how mycoplasmas may have evolved from these ancestors which had cell walls and large genomes. It is proposed that the initial step in this process was loss of the cell wall and conversion of the ancestral bacterium to an L-form. Fusion of L-forms would have resulted in a single cell that contained two or more complete genomes. It is thought that this bringing together of multiple genomes by cell fusion resulted in genetic recombination between genomes and loss of DNA segments from the cell. Data from bacterial systems are cited in support of this model. 相似文献
10.
The single, simple concept that natural selection adjusts distances between redox cofactors goes a long way towards encompassing natural electron transfer protein design. Distances are short or long as required to direct or insulate promiscuously tunneling single electrons. Along a chain, distances are usually 14 A or less. Shorter distances are needed to allow climbing of added energetic barriers at paired-electron catalytic centers in which substrate and the required number of cofactors form a compact cluster. When there is a short-circuit danger, distances between shorting centers are relatively long. Distances much longer than 14 A will support only very slow electron tunneling, but could act as high impedance signals useful in regulation. Tunneling simulations of the respiratory complexes provide clear illustrations of this simple engineering. 相似文献
11.
Analysis of Escherichia coli RecA interactions with LexA, lambda CI, and UmuD by site-directed mutagenesis of recA
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An early event in the induction of the SOS system of Escherichia coli is RecA-mediated cleavage of the LexA repressor. RecA acts indirectly as a coprotease to stimulate repressor self-cleavage, presumably by forming a complex with LexA. How complex formation leads to cleavage is not known. As an approach to this question, it would be desirable to identify the protein-protein interaction sites on each protein. It was previously proposed that LexA and other cleavable substrates, such as phage lambda CI repressor and E. coli UmuD, bind to a cleft located between two RecA monomers in the crystal structure. To test this model, and to map the interface between RecA and its substrates, we carried out alanine-scanning mutagenesis of RecA. Twenty double mutations were made, and cells carrying them were characterized for RecA-dependent repair functions and for coprotease activity towards LexA, lambda CI, and UmuD. One mutation in the cleft region had partial defects in cleavage of CI and (as expected from previous data) of UmuD. Two mutations in the cleft region conferred constitutive cleavage towards CI but not towards LexA or UmuD. By contrast, no mutations in the cleft region or elsewhere in RecA were found to specifically impair the cleavage of LexA. Our data are consistent with binding of CI and UmuD to the cleft between two RecA monomers but do not provide support for the model in which LexA binds in this cleft. 相似文献
12.
13.
F M Griffioen J H Smit-Vis P Brugman I J de Groot W G Sinnige 《Acta morphologica Neerlando-Scandinavica》1987,25(4):215-225
In order to study the effects of surgical procedures on the regeneration process in cleft palate, an artificial cleft was made in 4-weeks old female New Zealand rabbits. The 47 animals were divided into 5 groups: group 1: controls, group 2: cleft made in the bony palate, using a dental burr (phi 3 mm), group 3: cleft as in group 2, oral mucosa stitched, group 4: cleft made without perforating the nasal mucosa; oral mucosa stitched ("Veau"), group 5: cleft made as in group 4; before stitching the oral mucosa pieces of autologous rib bone were introduced into the cleft ("Schuchardt"). At the ages of 4, 5, 6, 8, 12, 18 and 24 weeks, one or two animals per group were sacrificed. The palatal region was microscopically studied using 10 mu paraffin sections stained according to Herovici. It was found that it is difficult to make a reproducible cleft on the histological level. A large interindividual variation in local damage due to the surgical procedure was observed; this might contribute to the variation in growth results of the facial skeleton reported in literature. Signs of excessive bone resorption were found. The presence of bone in places where sutural tissue should be present, observed in some growing animals, will contribute to reduction of palatal width, medial collapse of the palate and asymmetry of the facial skeleton. There appeared to be no striking differences between the three methods of repair, used in group 3, 4 and 5 respectively. 相似文献
14.
15.
Effect of voltage drop within the synaptic cleft on the current and voltage generated at a single synapse
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In a model of a single synapse with a circular contact zone and a single concentric zone containing receptor-gated channels, we studied the dependence of the synaptic current on the synaptic cleft width and on the relative size of the receptor zone. During synaptic excitation, the extracellular current entered the cleft and flowed into the postsynaptic cell through receptor channels distributed homogeneously over the receptor zone. The membrane potential and channel currents were smaller toward the cleft center if compared to the cleft edges. This radial gradient was due to the voltage drop produced by the synaptic current on the cleft resistance. The total synaptic current conducted by the same number of open channels was sensitive to changes in the receptor zone radius and the cleft width. We conclude that synaptic geometry may affect synaptic currents by defining the volume resistor of the cleft. The in-series connection of the resistances of the intracleft medium and the receptor channels plays the role of the synaptic voltage divider. This voltage dividing effect should be taken into account when the conductance of single channels or synaptic contacts is estimated from experimental measurements of voltage-current relationships. 相似文献
16.
HARRIETT E. SMITH-SOMERVILLE HOWARD E. BUHSE 《The Journal of eukaryotic microbiology》1984,31(3):373-380
The large cytopharyngeal pouch of the macrostomal form of Tetrahymena vorax, following the addition of calcium, can form a sealed, empty vacuole. The open cytostomal region of this cell, which averages about 16 μ in diameter, is closed by an upward (ventral) movement of the right and posterior ribbed walls, both of which project into the cytostomal cavity. At the same time, the anterior and left walls of the cytostome-cytopharyngeal complex move to the right, forming a diagonally (right to left) placed furrow in the floor of the buccal cavity as these walls meet. As a result of the movement, the edges of the single membrane-bounded cytopharyngeal pouch are brought together and fuse, producing the closed vacuole. Elements of the cytoskeleton appear to participate in the closure process. Three major groups of ribbed wall microtubules support the open cytostome. The anterior ribbed wall microtubules pass laterally along the anterior (dorsal) portion of the cytopharyngeal pouch to the left where they end in the specialized cytoplasm. Middle oral rib microtubules terminate at the right and posterior margin of the cytopharynx while microtubules from the most posterior region of the ribbed wall pass to the left terminating in the specialized cytoplasm. The fine filamentous reticulum, a striated reticulum that borders the right, posterior, and anterior margins of the cytostome-cytopharyngeal complex, is in an ideal position to participate in these movements. It is anchored anteriorly high up in the buccal cavity to the cross-connective between the third membranelle and the undulating membrane complex. It courses beneath the right and posterior ribbed walls and runs laterally along the anterior margin of the cytopharynx to the left side. Contraction or pulling of this reticulum would act to bring the microtubule-reinforced walls of the cytopharynx together permitting fusion of the cytopharyngeal pouch membranes to form a sealed vacuole. 相似文献
17.
Differences in face shape are considered a factor in cleft lip malformation. The purpose of this study was to analyze craniofacial growth in two strains: A/WySn with 28% cleft lip and C57BL/6J without cleft lip. Standardized photographs of 27 A/WySn and 25 C57BL/6J embryos with 34-46 somites (S) were taken in the superior, frontal, and lateral views. Landmarks were located and digitized for computerized analysis of growth change relative to somite number and at stages of face development before, during, and after primary palate closure. The results showed that both strains had similar overall growth patterns with increases in head width and face width, and decreases in nasal pit width. During early palatal closure in C57BL/6J mice, the nasal pit width was unchanged as brain width increased rapidly; and then later, the nasal pit width decreased as brain width increased slowly. However, during early closure in A/WySn mice, the nasal pit width decreased rapidly as brain width increased slowly; and then later, the nasal pit width was unchanged as brain width increased more rapidly. During early palatal closure, the narrower nasal pit width in A/WySn mice appeared to result from delayed growth of the supporting forebrain as the nasal pits become more medially positioned with normal face development. From the lateral view, the maxillary prominence depth was also smaller in the A/WySn strain during early palatal closure. This deficient forward growth of the maxillary prominences and the narrower positioning of the medial nasal prominences in A/WySn embryos appear to reduce the contact between the prominences and thus predispose this strain to cleft lip malformation. 相似文献
18.
《Journal of structural biology》2020,209(1):107413
ß-keratin chains contain a characteristic and homologous 34-residue sequence, which is believed to adopt a twisted ß-sheet conformation that assembles in an antiparallel manner with a similar sheet in a second chain to form a ß-sandwich. These sandwiches are, in turn, related to one another by a left-handed four-fold screw axis to generate a helical structure that forms the core of the 3.4 nm diameter filaments observed by electron microscopy and deduced from X-ray fibre diffraction. Recently, it has been shown that one ß-keratin chain, with a molecular weight approximately twice that of the majority of ß-keratin chains, is conserved across the lepidosaurs (lizards, snakes and tuatara). Uniquely, it contains four 34-residue repeats. Although this chain is a minor component the observation that the entire chain shows a high degree of sequence conservation between species suggests an important structural/functional role in vivo. Modelling shows that only six families of structures are physically possible. In three of these the repeats exist within a single filament and might therefore act in a filament nucleation role. In the second three families the repeats exist in two, three or four filaments, implying that their function may be to act as an inter-filament crosslinker, thereby providing lateral reinforcement to the epidermal appendage. The favoured model is one in which the first two repeats form a β-sandwich in one filament and the second two repeats form a β-sandwich in a neighbouring filament. Links between alternating up- and down-pointing β-sheets would provide optimum connectivity. 相似文献
19.
The V region sequences of two anti-DNA (A52, D42) and two anti-RNA (D44, D444) autoantibodies, derived from lupus prone NZB/NZW F1 female mice, were determined by mRNA sequencing. The sequences had the following features: 1) there was no clear sequence relationship between anti-DNA and anti-RNA antibodies; 2) there were no major similarities between any of the L chain sequences and each VL gene segment belonged to a different mouse VK subgroup; 3) the H chains of the two anti-RNA antibodies showed closely related sequences of VH gene segments and very similar third complementarity determining regions (CDR3); 4) the H chains of the two anti-DNA antibodies had VH segments belonging to different VH gene families but had a unique and similar combination of D segments and junctional sequences, suggesting a common recognition element for Ag and/or for idiotypic regulation in the H chain CDR3; and 5) the VH gene segment of one anti-DNA antibody (D42) was found to be very similar to the VH gene segment of a CBA mouse hybridoma antibody (6G6) which binds to the environmental Ag phosphocholine. The three-dimensional structure of the Fv-region of the anti-DNA antibody (D42) was modeled by computer and a stretch of poly(dT), ssDNA was docked to a cleft in the antibody combining site, formed by the three H chain CDR and by CDR1 and CDR3 of the L chain. The cleft is characterized by a preponderance of arginine and tyrosine residues, lining both the walls and base of the cleft. 相似文献
20.
Using molecular dynamics (MD) simulations, computational protein modifications, and a novel theoretical methodology that determines structural rigidity/flexibility (the FIRST algorithm), we investigate how molecular structure and dynamics of the glutamate receptor ligand binding domain (GluR2 S1S2) facilitate its conformational transition. S1S2 is a two-lobe protein, which undergoes a cleft closure conformational transition upon binding an agonist in the cleft between the two lobes; hence it is expected that the mechanism of this conformational transition can be characterized as a hinge-type. However, in the rigidity analysis one lobe of the protein is identified as a single rigid cluster while the other one is structurally flexible, inconsistent with a presumed mechanical hinge mechanism. Instead, we characterize the cleft-closing transition as a load and lock mechanism. We find that when two cross-cleft hydrogen bonds are disrupted the protein undergoes a rapid cleft opening transition. At the same time, the dynamical behavior of the cleft in the presence of the glutamate ligand is only weakly affected by the S652 peptide bond in its flipped conformation observed in the crystal structure. The residue E705 plays significant role in stabilization of the closed conformation via electrostatic interactions. The presence of the E705-K730 salt bridge seems to correlate strongly withthe cleft opening transition in the MD simulations. 相似文献