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)

A potent anticoagulant, anti-lipopolysaccharide (LPS) factor, found in limulus hemocytes inhibits the LPS-mediated activation of limulus coagulation cascade and shows an antibacterial action against R-types of Gram-negative bacteria (Morita, T., Ohtsubo, S., Nakamura, T., Tanaka, S., Iwanaga, S., Ohashi, K., and Niwa, M. (1985) J. Biochem. (Tokyo) 97, 1611-1620). The complete amino acid sequence of this substance was determined by sequencing the peptides obtained by selective proteolytic cleavage. The NH2-terminal end of anti-LPS factor was pyroglutamic acid. Anti-LPS factor had two variant residues at position 36 and the COOH-terminal end, respectively. The following sequence was assigned to anti-LPS factor, and it was also confirmed by fast atom bombardment mass spectrometry. less than EGGIWTQLALALVKNLATLWQSGDFQFLGHE (formula; see text) Limulus anti-LPS factor consisted of a single chain of 102 residues with 2 half-cystines in disulfide linkage. Its NH2-terminal region up to 20 residues was highly hydrophobic, and positively charged residues were clustered mainly within the disulfide loop. By searching the homologous sequence in known protein sequences with that of anti-LPS factor, we found a structural homology between anti-LPS factor and alpha-lactalbumin/lysozyme family.
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PMID:Primary structure of limulus anticoagulant anti-lipopolysaccharide factor. 371 Oct 91

The effect of iodide ion on the tryptophyl fluorescence of the homologous proteins lysozyme and alpha-lactalbumin in their native form, as well as in their modified structures and in fragments from these proteins was studied. By assessing the contribution to the total fluorescence of the exposed and buried Trp residues, and of the respective fluorescence quantum yields, the quantification of the number of Trp exposed to the solvent for all the species studied was possible. Both native proteins show an important increase in the number of Trp residues exposed to the solvent when treated with denaturing agents. The peptides L-II (aa 13-105) and alpha-I (aa 1-90) from lysozyme and alpha-lactalbumin, respectively, showed Trp residues with different degree of exposure, whereas the smaller fragments, L-III (aa 106-129) and alpha-II (aa 91-123), had all their Trp residues exposed to the solvent.
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PMID:Exposure of tryptophanyl residues in alpha-lactalbumin and lysozyme. Quantitative determination by fluorescence quenching studies. 376 24

Calcium performs a unique role in biology, achieving biological effects through highly specific interactions with and modulation of target proteins. It has been proposed that calcium-modulated proteins possess a characteristic, evolutionarily related, binding fold, known as the EF-hand. The high-resolution X-ray structure of alpha-lactalbumin reveals a Ca2+ binding fold that resembles an EF-hand only superficially and presumably has no evolutionary relationship with it. However, there is clear homology with the corresponding loop in c-type lysozyme (the 'parent' molecule of alpha-lactalbumin). This study, at 1.7 A resolution, represents one of the most accurate analyses of a calcium binding protein yet reported.
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PMID:Alpha-lactalbumin possesses a novel calcium binding loop. 378 75

The refolding kinetics of alpha-lactalbumin at different concentrations of guanidine hydrochloride have been investigated by means of kinetic circular dichroism and stopped-flow absorption measurements. The refolding reaction consists of at least two stages, the instantaneous accumulation of the transient intermediate that has peptide secondary structure and the subsequent slow process associated with formation of tertiary structure. The transient intermediate is compared with the well-characterized equilibrium intermediate observed during the denaturant-induced unfolding. Stabilities of the secondary structures against the denaturant, affinities for Ca2+, and tryptophan absorption properties of the transient and equilibrium intermediates were investigated. In all of these respects, the transient intermediate is identical with the equilibrium one, demonstrating the validity of the use of the equilibrium intermediate as a model of the folding intermediate. Essentially the same transient intermediate was also detected in the folding of lysozyme, the protein known to be homologous to alpha-lactalbumin but whose equilibrium unfolding is represented as a two-state reaction. The stability and cooperativity of the secondary structure of the intermediate of lysozyme are compared with those of alpha-lactalbumin. The results show that the protein folding occurring via the intermediate is not limited to the proteins that show equilibrium intermediates. Although the unfolding equilibria of most proteins are well approximated as a two-state reaction, the two-state hypothesis may not be applicable to the folding reaction under the native condition. Two models of protein folding, intermediate-controlled folding model and multiple-pathway folding model, which are different in view of the role of the intermediate in determining the pathway of folding, are also discussed.
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PMID:Evidence for identity between the equilibrium unfolding intermediate and a transient folding intermediate: a comparative study of the folding reactions of alpha-lactalbumin and lysozyme. 380 4

Both the Ca2+-bound and Ca2+-free forms of alpha-lactalbumin can assume essentially the same folded conformation as evidenced by similarity in their CD and proton n.m.r. spectra. Thermal unfolding followed by the aromatic CD has shown that the stability of the folded state is markedly enhanced by Ca2+ and that the stabilization is almost entirely entropic; addition of 0.1 mM Ca2+ shifts the transition temperature from 40 degrees to 62 degrees in 0.1M Na+ at pH 7.0. The enthalpy change of the unfolding, coincident between the two forms, is, however, significantly smaller than that known for lysozyme. The n.m.r. spectrum under the condition that both the forms of the protein are in the folded state reflects minor environmental changes of certain protons upon Ca2+ binding, and these changes are shown to afford useful probes for assessment of the location of the binding site. From the pH dependence and temperature dependence of the spectrum and also by using spin decoupling in the aromatic region (6.4-8.7 p.p.m.), it is shown that none of histidyl residues are affected and that at least two tryptophanyl ring protons experience environmental changes upon Ca2+ binding to the folded apo-protein. Effect of free excess Ca2+ on the spectrum has also shown that in native alpha-lactalbumin there is only one Ca2+-binding site that is detectable by the present method.
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PMID:Influence of Ca2+ binding on the structure and stability of bovine alpha-lactalbumin studied by circular dichroism and nuclear magnetic resonance spectra. 394 37

The changes in the absolute and relative contents of alpha- and kappa-caseins, lactoferrin, alpha-lactalbumin, serum albumin and lysozyme in human milk have been studied through the period of lactation. Protein fractions of 209 samples were analyzed by a discontinuous polyacrylamide gel electrophoresis method. beta- and kappa-caseins decreased from colostrum to mature milk although their relative percentages remained constant. They accounted for 12-15 and 9-13% of the total protein in human milk, respectively. Lactoferrin decreased in absolute and relative amounts with advancing lactation. This protein represented 32-19% of the human milk proteins. alpha-Lactalbumin slightly decreased from colostrum to transitional milk but there was an increase in mature milk by 16-30 days. The percentages of this protein in colostrum and mature milk were approximately 23 and 30%, respectively. Serum albumin also decreased with advancing lactation, but the differences between transitional and mature milk were not statistically significant. Lysozyme increased from colostrum to mature milk both in relative and absolute amounts. Colostrum contained about 262 micrograms/ml, and mature milk 1,246 micrograms/ml, representing 1.5 and 12.1% of total milk proteins.
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PMID:Changes in the protein fractions of human milk during lactation. 395 20

Refolding kinetics of two homologous proteins, lysozyme and alpha-lactalbumin, were studied by following the time-dependent changes in the circular dichroism spectra in the aromatic and the peptide regions. The refolding was initiated by 20-fold dilution of the protein solutions originally unfolded at 6 M guanidine hydrochloride, at pH 1.5 for lysozyme and pH 7.0 for alpha-lactalbumin at 4.5 degrees C. In the aromatic region, almost full changes in ellipticity that were expected from the equilibrium differences in the spectra between the native and unfolded proteins were observed kinetically. The major fast phase of lysozyme folding has a decay time of 15 s. The decay time of alpha-lactalbumin depends on the presence or absence of bound Ca2+: 10 s for the holoprotein and 100 s for the apoprotein. In the peptide region, however, most of the ellipticity changes of the two proteins occur within the dead time (less than 3 s) of the present measurements. This demonstrates existence of an early folding intermediate which is still unfolded when measured by the aromatic bands but has folded secondary structure as measured by the peptide bands. Extrapolation of the ellipticity changes to zero time at various wavelengths gives a spectrum of the folding intermediate. Curve fitting of the peptide spectra to estimate the secondary structure fractions has shown that the two proteins assume a similar structure at an early stage of folding and that the intermediate has a structure similar to that of partially unfolded species produced by heat and, for alpha-lactalbumin, also by acid and a moderate concentration of guanidine hydrochloride.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Comparison of the transient folding intermediates in lysozyme and alpha-lactalbumin. 399 96

The fluorescent behaviour and the photodynamic effect was studied in native and structurally modified lysozyme and alpha-lactalbumin. The Tyr residues in lysozyme and alpha-lactalbumin show different sensitivities to the photodynamic effect. The effect is zero in the case of Tyr from native lysozyme. In contrast, the Tyr residues in alpha-lactalbumin are susceptible to photooxidation, which indicates a greater degree of exposure to the solvent. The three His residues of alpha-lactalbumin have different degrees of exposure and show two different kinetics of photooxidation whereas the His residue of lysozyme is photooxidized with a single kinetic. Two photooxidation kinetics were obtained for the Trp residues of both native proteins, an indication that in both cases there are Trp residues that are differently exposed to the solvent. The wavelengths of maximum fluorescent emission of the Trp residues were different for the two proteins, an effect which can also be explained in terms of a difference in the environment of these residues. The modified form of these proteins emit at wavelengths longer than those of the native forms. When modified the proteins photooxidize with noticeably greater quantum yields.
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PMID:Photochemical reactivity of the homologous proteins alpha-lactalbumin and lysozyme. 401 49

The proton nuclear Overhauser effects of bovine alpha-lactalbumin were studied at 200 MHz by irradiation of an upfield ring current shifted methylene at -2.45 ppm (assigned to Ile-95) and two aromatic protons, Tyr-103 (8.36 ppm) and Trp-60 (5.85 ppm). The experimental results were consistent with a putative three-dimensional alpha-lactalbumin model [Warne, P. K., Momany, F. A., Rumball, S. V., Tuttle, R. W., & Scheraga, H. A. (1974) Biochemistry 13, 768-782], which predicted the close proximity of Ile-95, Tyr-103, Trp-60, and Trp-104. Several of the assignments correlated with those previously made from chemically induced dynamic nuclear polarization experiments [Berliner, L. J., & Kaptein, R. (1981) Biochemistry 20, 799-807]. Subtle differences in the structure of this hydrophobic box region in alpha-lactalbumin were found between the Ca(II) and apo forms of the protein. The existence of this "hydrophobic box" in alpha-lactalbumin was strikingly similar to that in lysozyme, as verified in solution.
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PMID:Structural elucidation of a hydrophobic box in bovine alpha-lactalbumin by NMR: nuclear Overhauser effects. 408 80

The ultraviolet circular dichroism spectra of human lysozyme are presented. Effects of pH and added inhibitor (N-acetyl-D-glucosamine) were examined and the results were compared with similar measurements of hen egg-white lysozyme. The near-ultraviolet CD spectral bands are substantially different in the human and hen egg-white enzymes. In addition to marked dissimilarities in the spectral interval 260-300 nm, an unusual CD band occurs at an anomalous wavelength (313 nm) in human lysozyme. The pH dependence of the latter suggests a possible interaction, absent in hen egg-white lysozyme, between a tryptophan and a tyrosine residue. Analysis of the spectra furthermore suggests lesser net rotational strengths of tryptophan bands in hen egg-white lysozyme than in human lysozyme, although the latter has one less tryptophan residue. The relationship between the CD spectra and the sequence differences of the proteins is discussed, as well as the CD spectra (published by others) of a closely related protein, bovine alpha-lactalbumin. Contributions of cystine residues to the spectra are examined in the light of possible differences in chirality of one of the four disulfide bridges.The far-ultraviolet CD spectra of human and egg-white lysozyme are quite similar, though not identical. In view of the pronounced differences in side-chain optical activity, and of the effect of pH variation on the far-ultraviolet CD spectrum of human lysozyme, it is likely that at least part of the observed difference in spectra is due to nonpeptide optical activity, and that the proteins have a secondary structure in common.
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PMID:Optical activity of human lysozyme. 527 53


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