title: Contribution of hydrogen bonds to the conformational stability of human lysozyme: calorimetry and X-ray analysis of six tyrosine --> phenylalanine mutants.
abstract: The contribution of hydrogen bonds to the conformational stability of human lysozyme was investigated by the combination of calorimetric and X-ray analyses of six Tyr --> Phe mutants. Unfolding Delta G and unfolding Delta H values of the Tyr --> Phe mutant proteins were changed by from +0.3 to -4.0 kJ/mol and from 0 to -16 kJ/mol, respectively, compared to those of the wild-type protein. The net contribution of a hydrogen bond at a specific site to stability (Delta Gwild/HB), considering factors affected by substitutions, was evaluated on the basis of X-ray structures of the mutant proteins. In the present study, one of six mutant proteins was suitable for evaluating the strength of the hydrogen bond. Delta Gwild/HB for the intramolecular hydrogen bond at Tyr124 was evaluated to be 7.5 kJ/mol. Results of the analysis of other mutants also suggest that hydrogen bonds of the hydroxyl group of Tyr, including the hydrogen bond with a water molecule, contribute to the stabilization of the human lysozyme.
authors.affiliation: Institute for Protein Research, Faculty of Pharmaceutical Sciences, Osaka University, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Yamagata
authors.forename: M
authors.initials: M
authors.lastname: Kubota
authors.forename: Y
authors.initials: Y
authors.lastname: Sumikawa
authors.forename: J
authors.initials: J
authors.lastname: Funahashi
authors.forename: K
authors.initials: K
authors.lastname: Takano
authors.forename: S
authors.initials: S
authors.lastname: Fujii
authors.forename: K
authors.initials: K
authors.lastname: Yutani
mesh_terms: D002152:Calorimetry, Differential Scanning; D018360:Crystallography, X-Ray; D006801:Humans; D006860:Hydrogen Bonding; D008958:Models, Molecular; D009113:Muramidase / Q000737:chemistry* / Q000235:genetics*; D016297:Mutagenesis, Site-Directed; D010649:Phenylalanine / Q000737:chemistry / Q000235:genetics*; D011487:Protein Conformation; D011489:Protein Denaturation; D017510:Protein Folding; D014443:Tyrosine / Q000737:chemistry / Q000235:genetics*
chemical_list: D014443:Tyrosine; D010649:Phenylalanine; D009113:Muramidase