title: Functional tolerance of Streptomyces subtilisin inhibitor toward conformational and stability changes caused by single-point mutations in the hydrophobic core.
abstract: Single amino acid mutations of Met103 in the hydrophobic core of a serine protease inhibitor, Streptomyces subtilisin inhibitor, caused little change in the inhibitory activity, as measured by the inhibitor constant, although some altered the thermodynamic stability of the protein considerably. (1)H NMR investigations showed that the conformational stress caused by the replacement of Met103 with Gly, Ala, Val, and Ile, namely, the effects of the cavities generated by replacements with smaller side-chains and of the steric distortions generated by beta-branched side-chains, caused considerable changes in the structural arrangement of the side-chains within the core. However, these structural changes were absorbed within the hydrophobic core, without distorting the structure of the reactive site essential for the protein function. These results provide an excellent example of the conformational flexibility of a protein core and the degree of its tolerance of an amino acid replacement. The results also reveal the crucially designed structural relationship between the core of the inhibitor and the enzyme-binding segment with the reactive site in a serine protease inhibitor.
authors.affiliation: Research Institute for Biological Sciences, Tokyo University of Science, Noda, Chiba 278-0022, Japan. oda@rs.noda.tus.ac.jp
authors.forename: Masayuki
authors.initials: M
authors.lastname: Oda
authors.forename: Atsuo
authors.initials: A
authors.lastname: Tamura
authors.forename: Kenji
authors.initials: K
authors.lastname: Kanaori
authors.forename: Shuichi
authors.initials: S
authors.lastname: Kojima
authors.forename: Kin-Ichiro
authors.initials: K
authors.lastname: Miura
authors.forename: Keiko
authors.initials: K
authors.lastname: Momma
authors.forename: Ben'ichiro
authors.initials: B
authors.lastname: Tonomura
authors.forename: Kazuyuki
authors.initials: K
authors.lastname: Akasaka
mesh_terms: D008715:Methionine / Q000378:metabolism; D008958:Models, Molecular; D019906:Nuclear Magnetic Resonance, Biomolecular; D017354:Point Mutation; D011487:Protein Conformation; D015842:Serine Proteinase Inhibitors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D013381:Subtilisins / Q000037:antagonists & inhibitors*; D013696:Temperature; D013816:Thermodynamics
chemical_list: D015842:Serine Proteinase Inhibitors; D008715:Methionine; D013381:Subtilisins