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 interaction between hen lysozyme and urea has been investigated using 1H nuclear magnetic resonance spectroscopy. Chemical shift changes for resonances of a number of residues in the vicinity of the active site of the protein have been observed in the presence of urea prior to denaturation. These shifts are similar to those induced in the hen lysozyme spectrum by the specific binding of N-acetylglucosamine (GlcNAc) in site C of the active site cleft, indicating that urea and GlcNAc induce a similar conformational change in the enzyme. This implies that the conformational changes experienced by the enzyme on the binding of GlcNAc oligosaccharides are the consequence of interactions, possibly hydrogen bonding, involving the N-acetyl group of the sugar residue bound in site C, rather than the result of contacts between the protein and the pyranose rings of the oligosaccharides. This suggests that hen lysozyme employs an induced fit type mechanism to discriminate for N-acetylated saccharides as substrates.
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PMID:1H nuclear magnetic resonance studies of the interaction of urea with hen lysozyme. Origins of the conformational change induced in hen lysozyme by N-acetylglucosamine oligosaccharides. 152 4

Hexagonal crystals of turkey egg white lysozyme have been examined for activity in order to evaluate their potential for use in time-resolved X-ray crystallographic experiments. Substrates used in this study were hexa-N-acetylglucosamine (hexa-GlcNAc) and a modified analogue of hexa-GlcNAc where the terminal sugar ring was opened by reduction with tritiated sodium borohydride. This gave a labeled beta-N-acetylglucosaminitol unit at the sixth position of the sugar chain and allowed easy quantitation of enzymatic cleavage on TLC plates. Using these substrates, it has been shown that turkey egg white lysozyme is enzymatically active in the crystal. Enzyme dispersed in the buffer surrounding the crystal does not show detectable activity under conditions relevant to an X-ray experiment. Unmodified hexa-GlcNAc is hydrolyzed into di-, tri-, and tetrasaccharides in the crystal. This cleavage pattern is different from that obtained with hen egg white lysozyme in solution and likely causes of the differences are discussed. The reduced radiolabeled oligosaccharide has a unique cleavage pattern with trisaccharides as the products. The specific activity of the enzyme with the radiolabelled analogue was 9.8 (+/- 1.0) x 10(-7) mmol/min/mg protein at 22 degrees C in the crystal.
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PMID:Activity of crystalline turkey egg white lysozyme. 155 84

An extracellular enzyme showing lytic activity on non-N-acetylated peptidoglycan has been isolated from Clostridium acetobutylicum ATCC 824. The lytic enzyme was purified to homogeneity by anion-exchange chromatography and gel filtration, with a recovery of 24%. The enzyme was monomeric and had an estimated molecular weight of 41,000 and an isoelectric point of 3.8. It has been characterized as a muramidase whose 23-amino-acid N terminus displayed 39% homology with the N,O-diacetyl muramidase of the fungus Chalaropsis sp. The muramidase hydrolyzed purified cell walls at an optimum pH of 3, with a maximum velocity of 9.1 mumol of reducing sugars released min-1 mg of muramidase-1 and a concentration of cell walls giving a half-maximum rate of 0.01 mg ml-1. Its activity was inhibited by glucosamine, N-acetylglucosamine, Hg2+, Fe3+, and Ag+ but not by choline. The muramidase-peptidoglycan complex rapidly dissociated before total hydrolysis of the chain and randomly reassociated on another peptidoglycan chain. The affinity of the muramidase was affected by the protein content and the acetylation of the cell wall.
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PMID:Purification and characterization of an extracellular muramidase of Clostridium acetobutylicum ATCC 824 that acts on non-N-acetylated peptidoglycan. 159 33

Chitinases isolated from membrane and cytosolic fractions of two mucoraceous fungi, Choanephora cucurbitarum and Phascolomyces articulosus, were investigated. The membrane-bound chitinase was isolated by Bio-Gel P-100 and DEAE Bio-Gel A chromatographic techniques. On SDS-PAGE the chitinase from both fungi migrated as a single band of M(r) 66 kDa. The cytosolic chitinase from the mycelial extracts of these fungi was separated by heat treatment, ammonium sulphate precipitation, and by affinity chromatography with regenerated chitin. SDS-PAGE showed two bands for each fungus with M(r) of 69.5 and 55 kDa in C. cucurbitarum and M(r) 69.5 and 53 kDa in Ph. articulosus. Chitinases, membrane bound or cytosolic, hydrolyzed regenerated chitin, colloidal chitin, glycol chitin, N,N'-diacetylchitobiose, and N,N',N"-triacetylchitotriose. Heavy metals, inhibitors, and N-acetylglucosamine inhibited chitinase activity, whereas trypsin and an acid protease enhanced its activity. Chitinase preparations showed lysozyme activity that was inhibited by histamine but not by N-acetylglucosamine. There was no N-acetylglucosamanidase activity, but beta-1,3 glucanase activity was found in cytosolic preparations only. Despite slight differences in their molecular mass, both the membrane-bound and cytosolic chitinases showed similarities in substrate utilization, response to inhibitors, and activation by trypsin and acid protease; pH and temperature optima also were similar.
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PMID:Cytosolic and membrane-bound chitinases of two mucoraceous fungi: a comparative study. 161 60

The indole C-2(delta 1) carbon of Trp 62 in hen egg-white lysozyme was selectively labeled with 13C through a series of reactions involving N'-formylkynurenine 62-lysozyme with K13CN, NaBH4-reduction, and acid-catalyzed dehydration. [delta 1-13C]Trp 62-lysozyme in which Trp 62 is labeled with 90% 13C has the same chemical and enzymatic properties as the native protein. The reverted lysozyme gave a single 13C-NMR signal at 125 ppm. pH-titration of the 13C signal indicated a transition at pH 3.9 for the free enzyme. In the presence of (GlcNAc)3, the resonance signals were shifted 0.5-1 ppm upfield, and the transitions in the titration curve were observed at pH 3.9 and 6.5. Asp 52 and Glu 35 were assigned to the groups with pKas of 3.9 and 6.5, respectively. In [2-13C]AHT 62-lysozyme, which has 3-(2-amino-3-hydroxy-3H-[2-13C]indol-3-yl)alanine (AHT) at position 62, AHT 62 behaved quite differently from Trp 62 on pH-titration of the 13C-label. These results suggest that a conformational change around Trp 62 is induced upon ionization of the catalytic residue and that the structural flexibility of the side chain of this aromatic residue in the substrate binding site is closely related to the function of lysozyme.
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PMID:Site-specific 13C-labeling of Trp 62 in hen egg-white lysozyme: preparation and 13C-NMR titration of [delta 1-13C]Trp 62-lysozyme. 176 25

The structure of lysozyme from guinea hen egg white (GEWL), which differs from hen egg white lysozyme (HEWL) by ten amino acid substitutions, was investigated by nuclear magnetic resonance (NMR) spectroscopy. GEWL and HEWL were very similar to each other in their tertiary structure as judged from the profile of 1H-NMR spectra, pH titration, and an N-acetylglucosamine trisaccharide [(GlcNAc)3 binding experiment. However, we have noticed several characteristics which distinguish GEWL from HEWL. The signal of Trp 108 indole N1H of GEWL was shifted upfield by about 0.3 ppm when compared with that of HEWL, and its hydrogen exchange was faster than that of HEWL. The pKa values of Glu 35 estimated from the pH titration curve of Trp 108 indole N1H were different between GEWL and HEWL. From a careful examination of spectral changes caused by (GlcNAc)3 binding, the changes in the chemical shift values of Trp 28 C5H and Asn 59 alpha CH of GEWL were found to be slightly larger than those of HEWL. Ile 55 of HEWL is replaced by valine in GEWL. Such a replacement may affect the neighboring hydrogen bonding between the main chain C = O of Leu 56 and Trp 108 indole N1H, resulting in a change in the microenvironment of the substrate-binding site near Trp 108.
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PMID:1H-NMR study on the structure of lysozyme from guinea hen egg white. 179 91

The role of aspartic acid 53 of human lysozyme (peptidoglycan N-acetylmuramoylhydrolase, EC 3.2.1.17) has been investigated by a site-directed mutagenesis. In order to clarify the importance of precise positioning of the negatively charged carboxylate group in the active site geometry, both the three-dimensional structure and the enzymatic function of glutamic acid 53 human lysozyme (Glu-53 human lysozyme) have been characterized in comparison with those of wild type enzyme. Glu-53 human lysozyme was crystallized and analysed by X-ray crystallography. No remarkable difference in the conformation of whole molecule except the side chain of 53rd residue was observed. In spite of full retention of the binding activities against either beta-1,4-linked trisaccharide of N-acetylglucosamine ((GlcNAc)3) or the corresponding hexasaccharide ((GlcNAc)6), the conversion of Asp-53 to Glu reduced the enzymatic activities against both bacterial cell substrate and p-nitrophenyl penta-N-acetyl-beta(1----4)-chitopentaoside (p-NO2-(GlcNAc)5) to a few percent of the activities of wild type enzyme. Calculation of electrostatic potential around the reaction center predicted that no significant change in pKa of Glu-35 was caused by the mutation. These results indicate that the precise positioning of the negatively charged carboxylate in the geometry of reaction center is essential for the rate enhancement in the catalytic action of lysozyme, and suggest that Asp-53 of human lysozyme participates in the catalytic action not simply in an electrostatical manner but partly in a nucleophilical manner.
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PMID:The importance of precise positioning of negatively charged carboxylate in the catalytic action of human lysozyme. 191 46

Previous findings have demonstrated the presence of muramic acid and the lack of sialic acid in gastropod glycoconjugates from different tissues. The present study investigated the composition of muramyl derivatives in Mollusca Gastropoda tissue from the foot, mantle and periesophageal ganglia, using HRP-labeled lectins (LTA, UEA I, GSA IB4, GSA II, DBA, SBA, RCA II, WGA, PNA, ConA) and glycosidase digestion (neuraminidase, lysozyme, alpha-L-fucosidase, beta-N-acetylglucosaminidase, alpha-N-acetylgalactosaminidase). Muramyl derivatives from the tissue examined showed some differences related to the composition of the terminal disaccharides. Indeed, foot and mantle mucocytes exhibited muramic acid in a terminal position, linked to (subterminal) N-acetylgalactosamine, whereas in neuron cells muramic acid was present in an internal position and linked to N-acetylglucosamine. Diversities also occurred between foot and mantle mucocytes with respect to the receptor sugar for penultimate N-acetylgalactosamine.
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PMID:Identification of muramyl derivatives in Mollusca Gastropoda tissue. 191 77

Adherent cultures of rat peritoneal macrophages secrete lysozyme and the lysosomal marker enzymes beta-glucuronidase, beta-N-acetylglucosaminidase and acid phosphatase; the levels of secreted lysosomal cathepsin D, however, were found to be insignificant. Incubation of the cells at 4 degrees C for 15 min with yeast mannan or with 50 mM mannose, methyl alpha-glucopyranoside, or N-acetylglucosamine caused the concentration of cathepsin D in the culture medium to increase 30-40-fold; mannose-6-phosphate had no effect. 125I-labeled cathepsin D was prepared and the binding constant to the macrophage cell surface was determined to be KD = 27 nM. The data suggest that cathepsin D binds to the mannose receptor of macrophages and that binding to this receptor is not in equilibrium with the bulk medium.
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PMID:Binding of cathepsin D to the mannose receptor on rat peritoneal macrophages. 193 26

Lysis of Escherichia coli induced by either D-cycloserine, moenomycin, or penicillin G was monitored by studying murein metabolism. The levels of the soluble murein precursor UDP-N-acetylmuramyl-L-alanyl-D-glutamyl-m-diaminopimelyl-D-alanyl- D-alanine (UDP-MurNAc-pentapeptide) and the carrier-linked MurNAc-(pentapeptide)-pyrophosphoryl-undecaprenol as well as N-acetylglucosamine-beta-1,4-MurNAc-(pentapeptide)-pyrophosphoryl- undecaprenol varied in a specific way. In the presence of penicillin, which is known to interfere with the cross-linking of murein, the concentration of the lipid-linked precursors unexpectedly decreased before the onset of lysis, although the level of UDP-MurNAc-pentapeptide remained normal. In the case of moenomycin, which specifically blocks the formation of the murein polysaccharide strands, the lipid-linked precursors as well as UDP-MurNAc-pentapeptide accumulated as was expected. D-Cycloserine, which inhibits the biosynthesis of UDP-MurNAc-pentapeptide, consequently caused a decrease in all three precursors. The muropeptide composition of the murein showed general changes such as an increase in the unusual DL-cross bridge between two neighboring meso-diaminopimelic acid residues and, as a result of uncontrolled DL- and DD-carboxypeptidase activity, an increase in tripeptidyl and a decrease in tetrapeptidyl and pentapeptidyl moieties. The average length of the glycan strands decreased. When the glycan strands were fractionated according to length, a dramatic increase in the amount of single disaccharide units was observed not only in the presence of penicillin but also in the presence of moenomycin. This result is explained by the action of an exo-muramidase, such as the lytic transglycosylases present in E. coli. It is proposed that antibiotic-induced bacteriolysis is the result of a zipperlike splitting of the murein net by exo-muramidases locally restricted to the equatorial zone of the cell.
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PMID:Analysis of murein and murein precursors during antibiotic-induced lysis of Escherichia coli. 204 64


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