Multiple role of hydrophobicity of tryptophan-108 in chicken lysozyme: structural stability, saccharide binding ability, and abnormal pKa of glutamic acid-35.

摘要: Trp108 of chicken lysozyme is in van der Waals contact with Glu35, one two catalytic carboxyl groups. The role function and stability was investigated by using mutant lysozymes secreted from yeast. By the replacement less hydrophobic residues, Tyr (W108Y lysozyme) Gln (W108Q lysozyme), activity, saccharide binding ability, stability, pKa Glu35 were all decreased a decrease hydrophobicity residue 108. Namely, at pH 5.5 40 degrees C, activities W108Y W108Q against glycol chitin 17.3 1.6% that wild-type lysozyme, their dissociation constants for trimer N-acetyl-D-glucosamine 7.4 309 times larger than respectively. For reversible unfolding 3.5 30 stable 1.4 3.6 kcal/mol, As values found to be lower 0.2 0.6 unit, also 6.1 5.4 presence 1-3 M guanidine hydrochloride, or substitution Asn Asp52, another group. Thus, both electrostatic interaction Asp52 are equally responsible abnormally high (6.1) compared (4.4) normal glutamic acid residue.(ABSTRACT TRUNCATED AT 250 WORDS)