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Peptides from rat liver aldehyde dehydrogenase (AIDH) induced by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) treatment match the AIDH structure from HTC rat hepatoma cells (HTC-AIDH) at all positions examined, indicating induction of the same gene product by two independent routes. This 452 amino acid residue, class 3 AIDH structure differs substantially from the 500-residue AIDH structures isolated from normal liver cytosol (class 1) and mitochondria (class 2). Despite a 29.8% identity in 429 overlapping amino acids vs the human class 1 enzyme (27.7% vs class 2), neither the N- nor C-termini coincide, and gaps are introduced to optimize the alignment. Two residues placed in the active site of human liver AIDH by chemical modification, Cys-302 and Glu-268, are conserved in class 3 AIDH as Cys-243 and Glu-209. Cys-243/302 is the only cysteine residue conserved in all known AIDH structures. Gly-245 and Gly-250 of class 1/2 AIDHs, fitting the patterns of glycine residues in coenzyme binding fold of other dehydrogenases, are also conserved. Otherwise, Cys-49, Cys-162, and Glu-487, to which functional importance has also been ascribed, are not retained in the class 3 structure. Overall, a high conservation of Gly, Pro, and Trp and similar patterns of predicted secondary structure indicate general conservation of tertiary structure, as noted with other distantly related proteins. Three exon boundaries from the human liver mitochondria AIDH gene directly correspond to the N-terminus of the rat class 3 protein and to two of the gaps in the alignment.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
3.
Pulse-labelling of mouse mastocytoma cell cultures, established from ascites fluid, with inorganic [35S]sulphate for 1 h yielded labelled heparin proteoglycan containing polysaccharide chains of Mr 60,000-100,000. After chase incubation for 24 h most of the 35S appeared in intracellular polysaccharide fragments similar in size to commercially available heparin, Mr 5000-25,000, as indicated by gel chromatography. Products isolated from cultures after 6 h of chase incubation consisted of partially degraded free polysaccharide chains and, in addition, residual proteoglycans that were of smaller size than the proteoglycans initially pulse-labelled. The polysaccharide chains released by alkali treatment from the residual chase-incubated proteoglycans were of the same size as the chains derived from proteoglycans after 1 h of pulse labelling. These results suggest that the intracellular degradation of heparin proteoglycan to polysaccharide fragments is initiated by release of intact polysaccharide chains, probably by action of a peptidase, and is pursued through cleavage of these chains by an endoglycosidase. An endoglucuronidase with stringent substrate specificity [Thunberg, Bäckström, Wasteson, Ogren & Lindahl (1982) J. Biol. Chem. 257, 10278-10282] has previously been implicated in the latter step. Cultures of more purified mastocytoma cells (essentially devoid of macrophages) did not metabolize [35S]heparin proteoglycan to polysaccharide fragments, but instead accumulated free intact polysaccharide chains, i.e. the postulated intermediate of the complete degradation pathway. When such purified cells were co-cultured with adherent mouse peritoneal cells, presumably macrophages, formation of polysaccharide fragments was observed. It is tentatively proposed that the expression of endoglucuronidase activity by the mast cells depends on collaboration between these cells and macrophages. 相似文献
4.
K99 Fimbriae from enterotoxigenicEscherichia coli (ETEC) were found to bind specifically to sialic acid, as measured in a haemagglutination inhibition assay using the intact bacteria and human erythrocytes. The affinity forN-glycolylneuraminic acid was about twice that ofN-acetylneuraminic acid (NeuAc), and other monosaccharides were found to be at least ten-fold less effective as inhibitors. The specificity was found to depend on electrostatic interaction where the carboxyl group and its orientation plays an important role. 2--Benzyl-NeuAc was a better inhibitor than 2--methyl-NeuAc suggesting a hydrophobic patch near the binding site on the protein. Axially oriented hydroxyl groups as in 4-epi-NeuAc and 3-hydroxy-NeuAc seemed to participate in binding since these derivatives were better inhibitors thanN-acetylneuraminic acid. K99 was found to have a higher affinity for 4-O-acetyl-NeuAc and lower affinity forN-acetylneuraminic acid withO-substituents at C7-C9 as compared toN-acetylneuraminic acid. Hence, the degree ofO-acetylation of sialic acid in the mucosa of the small intestine may influence colonization and determine susceptibility to infection. 相似文献
5.
Anti-thrombin activities of heparin. Effect of saccharide chain length on thrombin inhibition by heparin cofactor II and by antithrombin. 总被引:1,自引:0,他引:1 下载免费PDF全文
The interactions of two proteinase inhibitors, heparin cofactor II and antithrombin, with thrombin are potentiated by heparin. Using two methods, we have studied the potentiating effects of a series of heparin (poly)saccharides with high affinity for antithrombin and mean Mr ranging from approx. 1700 to 18,800. First, catalytic amounts of heparin (poly)saccharide were added to purified systems containing thrombin and either heparin cofactor II or antithrombin. Residual thrombin activity was determined with a chromogenic substrate. It was found that only the higher-Mr polysaccharides (Mr greater than 8000) efficiently catalysed thrombin inhibition by heparin cofactor II, there being a progressive catalytic effect with increasing Mr of the polysaccharide. Weak accelerating effects were noted with low-Mr saccharides (Mr less than 8000). This contrasted with the well-characterized interaction of heparin with antithrombin and thrombin, where heparin oligosaccharides of Mr less than 5400 had absolutely no ability to accelerate the reaction, while (poly)saccharides of Mr exceeding 5400 showed rapidly increasing catalytic activity with increasing Mr. Secondly, these and other heparin preparations were added in a wide concentration range to plasma with which 125I-labelled thrombin was then incubated for 30 s. Inhibited thrombin was determined from the distribution of labelled thrombin amongst inhibitor-thrombin complexes, predominantly antithrombin-thrombin and heparin cofactor II-thrombin complexes. In this situation, where the inhibitors competed for thrombin and for the (poly)saccharides, it was found that, provided the latter were of high affinity for antithrombin and exceeded a Mr of 5400, thrombin inhibition in plasma was mediated largely through antithrombin. Polysaccharides of Mr exceeding 8000 that were of low affinity for antithrombin accelerated thrombin inhibition in plasma through their interaction with heparin cofactor II. High concentrations of saccharides of Mr 1700-5400 exhibited a size-dependent acceleration of thrombin inhibition, not through their interaction with antithrombin, but through their interaction with heparin cofactor II. 相似文献
6.
H-2M3 encodes the MHC class I molecule presenting the maternally transmitted antigen of the mouse 总被引:6,自引:0,他引:6
Mta, the maternally transmitted antigen of mice, is a hydrophobic, N-formylated mitochondrial peptide, MTF, presented on the cell surface to cytotoxic T lymphocytes by a novel major histocompatibility complex class I molecule, encoded by H-2M3. We have cloned and sequenced two alleles of M3, which differ in their ability to present MTF despite greater than 99% identity in the coding regions. M3 is as divergent from classical, antigen-presenting H-2 molecules as from other class I genes of the Hmt and the Qa/Tla regions. Amino acids critical for folding of class I molecules are conserved in M3. Noncharged amino acids lining the peptide-binding groove and phenylalanine 171 may explain the unique interaction with MTF, and leucine 95 appears critical for immunological activity. 相似文献
7.
Monoclonal antibodies specific for oligosaccharides prepared by partial nitrous acid deamination of heparin 总被引:5,自引:0,他引:5
G Pejler U Lindahl O Larm E Scholander E Sandgren A Lundblad 《The Journal of biological chemistry》1988,263(11):5197-5201
Monoclonal antibodies were raised against a conjugate between heparin oligosaccharides and human serum albumin. The oligosaccharides were prepared by partial nitrous acid degradation of heparin and were coupled to human serum albumin by reductive amination. Characterization of the antibodies secreted by one of the resulting clones showed that they recognize a determinant present in the oligosaccharide antigen, but not in intact heparin, nor in a variety of related polysaccharides. Degradation of heparin by nitrous acid generates a 2,5-anhydro-D-mannose residue at the reducing end of the resulting oligosaccharides, and it is concluded that this structure is essential for interaction with the antibodies. Reduced oligosaccharides (containing a terminal anhydromannitol residue) are also active. After gel chromatography of partially degraded heparin, the smallest components capable of binding to the antibodies were found in a tetrasaccharide fraction. Affinity chromatography on immobilized monoclonal antibodies separated this tetrasaccharide fraction into distinct populations of binding and nonbinding species. Structural analysis showed that the tetrasaccharide fraction that bound to the monoclonal antibodies contained one single component with the structure IdoA(2-OSO3)-GlcNSO3 (6-OSO3)-IdoA(2-OSO3)-aManR(6-OSO3), whereas the fraction that did not bind to the antibodies contained a mixture of different structures. 相似文献
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Initiation of DNA replication in Escherichia coli: RNase H-deficient mutants do not require the dnaA function 总被引:9,自引:0,他引:9
Summary A series of temperature-resistant revertants were isolated from strains of Escherichia coli K12 carrying a temperature-sensitive mutation in the dnaA gene. Four independent revertants were found which still carry the original ts mutation. The ability of these strains to grow at high temperature is due to a suppressor mutation, called sin. All four sin mutations are located between the genes metD and proA on the genetic map of E. coli, which suggests that they all affect the same gene. The sin suppressors, which were isolated for their ability to suppress one dnaA mutation, are also able to suppress three other temperature-sensitive dnaA mutations, but they are not able to suppress mutations in either of the two genes dnaB or dnaC. The sin suppressors alone do not confer any particular phenotype on bacteria, but they are deficient in the enzyme RNase H. On the basis of these findings we propose that the function of the dnaA protein is to protect a DNA-RNA hybrid at the origin of replication against RNase H. 相似文献