Structural studies of mutants of the lysozyme of bacteriophage T4: The temperature-sensitive mutant protein Thr157 → Ile

摘要: Abstract To understand the roles of individual amino acids in folding and stability globular proteins, a systematic structural analysis mutants lysozyme bacteriophage T4 has been undertaken. The isolation, characterization, crystallographic refinement temperature-sensitive which threonine 157 is replaced by isoleucine reported here. This mutation reduces temperature midpoint reversible thermal denaturation transition 11 deg.C at pH 2.0. Electron density maps showing differences between wild-type mutant X-ray crystal structures have obvious features corresponding to substitution isoleucine. There little difference electron remainder molecule, indicating that changes are localized site mutation. Highresolution structure confirms it very similar lysozyme. largest conformational γ-carbon residue side-chain Asp159, shift 1.0 A 1.1 A, respectively. In enzyme, γ-hydroxyl group Thr157 participates network hydrogen bonds. Substitution with an disrupts this set water molecule bound vicinity Thr155 partially restores bond structure, but buried main-chain amide Asp159 not near acceptor. unsatisfied hydrogen-bonding potential most reason for reduction protein.