Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.2.1.17 (lysozyme)
21,489 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The energetics of a salt bridge formed between the side chains of aspartic acid 70 (Asp70) and histidine 31 (His31) of T4 lysozyme have been examined by nuclear magnetic resonance techniques. The pKa values of the residues in the native state are perturbed from their values in the unfolded protein such that His31 has a pKa value of 9.1 in the native state and 6.8 in the unfolded state at 10 degrees C in moderate salt. Similarly, the aspartate pKa is shifted to a value of about 0.5 in the native state from its value of 3.5-4.0 in the unfolded state. These shifts in pKa show that the salt bridge is stabilized 3-5 kcal/mol. This implies that the salt bridge stabilizes the native state by 3-5 kcal/mol as compared to the unfolded state. This is reflected in the thermodynamic stability of mutants of the protein in which Asp70, His31, or both are replaced by asparagine. These observations and consideration of the thermodynamic coupling of protonation state to folding of proteins suggest a mechanism of acid denaturation in which the unfolded state is progressively stabilized by protonation of its acid residues as pH is lowered below pH 4. The unfolded state is stabilized only if acidic groups in the folded state have lower pKa values than in the unfolded state. When the pH is sufficiently low, the acid groups of both the native and unfolded states are fully protonated, and the apparent unfolding equilibrium constant becomes pH independent. Similar arguments apply to base-induced unfolding.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:pH-induced denaturation of proteins: a single salt bridge contributes 3-5 kcal/mol to the free energy of folding of T4 lysozyme. 233 7

Nonenzymic deamidation of amides in proteins (lysozyme and albumin) under conditions which imitate physiological ones has been experimentally established with subsequent asparagine-dependent autofragmentation of the polypeptide chain.
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PMID:[Non-enzymatic deamidation and autofragmentation of lysozyme and albumin under physiological conditions]. 318 64

The complete primary structure of donkey lysozyme has been established by pulsed liquid-phase sequencing of tryptic and chymotryptic peptides isolated by RP-HPLC. The positions of the Cys residues were identified by labeling the Cys residues with DABIA-reagent. Donkey lysozyme is a c-type lysozyme which is 129 amino acids long. It exhibits 50% homology to the human protein. We observe the full Ca(II) binding site suggested for the homologous alpha-lactalbumines. Although horse lysozyme has been reported to contain asparagine in position 61, which was in conflict with the three-dimensional structure of lysozyme, all other known c-type lysozymes, including donkey, contain Ser 61.
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PMID:The primary structure of donkey (Equus asinus) lysozyme contains the Ca(II) binding site of alpha-lactalbumin. 324 41

In a two-step process, esterification and ammonolysis, Glu-35 and Asp-52 in lysozyme were amidated to glutamine and asparagine residues. Since the side chains of glutamine and asparagine are almost equal in size to those of glutamic acid and aspartic acid, these conversions would provide appropriate derivatives to elucidate the catalytic participations of these residues. The enzymatic activities of the resulting [Gln35]lysozyme and [Asn52]lysozyme were found to be less than 4% of that of native lysozyme in a pH range of 3.4-8.0. As these derivatives were inactive, we could determine the dissociation constants (Ks values) for the binding of beta-1,4-linked n-mer, a hexasaccharide of N-acetyl-D-glucosamine, to [Gln35]lysozyme and [Asn52] lysozyme. The values of Ks at pH 5.5 and 40 degrees C were 1.6 X 10(-5) M for [Gln35]lysozyme and 2.7 X 10(-5) M for [Asn52]lysozyme. These values are similar to that for native lysozyme. The results are direct proof for the involvements of Glu35 and Asp52 in the catalytic action of lysozyme. A method for ammonolysis of ester groups in proteins in liquid ammonia is described and will be useful for amidation of carboxyl groups of proteins.
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PMID:Chemical mutations of the catalytic carboxyl groups in lysozyme to the corresponding amides. 375 81

The mechanism of irreversible thermoinactivation of an enzyme has been quantitatively elucidated in the pH range relevant to enzymatic catalysis. The processes causing irreversible inactivation of hen egg-white lysozyme at 100 degrees C are deamidation of asparagine residues, hydrolysis of peptide bonds at aspartic acid residues., destruction of disulfide bonds, and formation of incorrect (scrambled) structures; their relative contributions depend of the pH.
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PMID:The mechanisms of irreversible enzyme inactivation at 100C. 400 42

A pair of frame shift mutations in the lysozyme gene of bacteriophage T4 results in the substitution of a glutamyl-tyrosyl sequence for the asparagine residue that is the penultimate amino-terminal amino acid in the lysozyme of the wild-type strain. One of the mutations has been identified as the insertion of two bases, the other as the insertion of a single base.
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PMID:Frame shift mutations near the beginning of the lysozyme gene of bacteriophage T4. 568 21

A radiochemical method for the determination of the amino terminus on very small amounts (0.5-5 nmol) of protein is described. The high sensitivity of the method is achieved by using undiluted 1-fluoro-2,4-dinitro-[3,5-3H]benzene [( 3H]Dnp-F) as the labelling reagent under conditions in which a maximum amount of radioactive label is incorporated. Chemical homogeneity is achieved by reacting with excess unlabelled Dnp-F. High recovery is obtained by adding Dnp-albumin as carrier protein. A mixture of Dnp 14C-labelled amino acids is added prior to hydrolysis and identification of the amino terminus is made on the basis of the 3H/14C ratios of the separated Dnp-amino acids. The method was tested on insulin, pancreatic ribonuclease, and lysozyme which gave high 3H/14C ratios only in the expected amino-terminal amino acids. Application to multiple forms of poly(C)-avid ribonuclease gave only amino-terminal lysine. Two of four putative isozymes of 17 beta-hydroxysteroid dehydrogenase had serine as the amino terminus while the other two had aspartic acid or asparagine.
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PMID:A highly sensitive method for identification of amino termini of proteins: application to multiple forms of poly(C)-avid ribonuclease and 17 beta-hydroxysteroid dehydrogenase. 630 40

We have investigated the effect of 12 solvents and several amino acids on the fluorescence of O-(4-methylumbelliferyl)-glycosides. We showed that: i) the fluorescence quenching is not related to the dielectric constant of the solvents: the fluorescence intensity was maximal in water (d = 80) and in acetic acid (d = 6.2) and was at least ten times lower in acetone (d = 21) and in dioxane (d = 2.2); ii) the fluorescence of O-(4-methylumbelliferyl)-N-acetyl-beta-glucosaminide is not quenched in the presence of various amino acids including arginine, asparagine, aspartate, histidine, leucine, phenylalanine and proline; iii) the fluorescence of O-(4-methylumbelliferyl)-glycoside is quenched by sulfur, phenol and indole amino acids or derivatives containing sulfur, phenol or indole groups. The changes in fluorescence intensities of O-(4-methylumbelliferyl)-glycosides upon binding to concanavalin A, wheat germ agglutinin and lysozyme are discussed with regard to the amino acid content of their binding sites.
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PMID:Protein-sugar interactions: environmental effect on the fluorescence of O-(4-methylumbelliferyl)-glycosides. 668 82

Since it has been uncertain whether residue 103 in hen egg-white lysozyme is aspartic acid or asparagine, we reexamined the identity of this residue. To avoid complication, the tryptic peptide T-13 (Ile 98-Arg 112) was further cleaved. The peptide containing residues Gly 102-Arg 112 was obtained by tryptic digestion of lysozyme modified at Asp 101 with diethylenetriamine. The peptide containing residues Ile 98-homoserine 105 was obtained by BrCN treatment of peptide T-13. Both Edman degradation of the former peptide and carboxypeptidase X digestion of the latter peptide identified residue 103 in hen egg-white lysozyme as asparagine.
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PMID:Identification of residue 103 in hen egg-white lysozyme. 730 22

The chemical modification of Asp101 which is located at the upper end-most site (site A) of the binding cleft of hen egg white lysozyme affects the sugar residue binding of the midmost site (site C) in addition to that of site A, and results in the considerable decrease in the enzymic activity [Fukamizo, T., Hayashi, K. & Goto, S. (1986) Eur. J. Biochem. 158, 463-467]. In the present study, Asp101 was modified with histamine and converted to [2-imidazol-4(5)-ylethyl]asparagine. Contrary to the findings described above, the specific activity of the modified lysozyme was higher than that of the native lysozyme by a factor of about two, and the loss of sugar residue binding ability caused by the modification was found to be restricted to site A. From the H-NMR spectra of the modified lysozyme, the pKa value of the imidazolylethyl group covalently attached to Asp101 was 7.1, and was higher than that of N-acetylhistidinemethylamide (6.65). This indicates that the imidazolylethyl moiety is not exposed to the solvent but adheres to the surface of the lysozyme molecule in an unidentified manner. When N-acetylglucosamine trisaccharide [GlcNAc)3] was added to the modified lysozyme, the 1H-NMR signals of H2 and H4 of the imidazolylethyl group were strongly affected. This indicates that the imidazolylethyl moiety is located near (GlcNAc)3 binding region. When the H gamma signal of Ile98 was saturated, nuclear Overhauser effects were observed on H2 and H4 resonances of the imidazolylethyl moiety. NOE was also observed on the signal of Trp63 H6 upon the saturation of the H4 signal of the imidazolylethyl moiety. Thus, the imidazolylethyl moiety should be located near Trp63 and Ile98, which are in the hydrophobic box most proximal to the sugar binding cleft. This situation of the imidazolylethyl moiety did not result in steric hindrance to the sugar residue binding at sites B and C. The modification affected only the sugar residue binding at site A, and resulted in the enhanced activity.
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PMID:Hen-egg-white lysozyme modified with histamine. State of the imidazolylethyl group covalently attached to the binding site and its effect on the sugar-binding ability. 762 85


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