title: Substrate-induced changes in protease active site conformation impact on subsequent reactions with substrates.
abstract: Enzymatic catalysis of biochemical reactions is essential to all living systems. The "lock and key" and "induced fit" models were early contributions to our understanding of the mechanisms involved in the reaction between an enzyme and its substrate. However, whether a given substrate-induced conformation is rigid or remains flexible has not yet been determined. By measuring the enzyme activity and intrinsic fluorescence of a nonspecific Eisenia fetida protease-I with different chromogenic substrates, we show that in subsequent reactions of protease with substrates, both the "lock and key" and "induced fit" mechanisms are used depending on the degree of conformational change required. Chromozym-Th- or chromosym-Ch-induced protease conformations were unable to bind chromozym-U. The chromosym-U-induced protease conformation remained flexible and could be further induced by chromozym-Th and chromozym-Ch. When low concentrations of guanidine HCl were used to disturb the conformation of the enzyme, only small changes in intrinsic fluorescence of the chromozym-Th-induced protease were detected, in contrast to the native enzyme whose intrinsic fluorescence markedly increased. This indicates that the substrate-induced enzyme was relatively rigid compared with the native protease. Utilizing a lock and key mechanism for secondary substrate reactions may have adaptive value in that it facilitates high efficiency in enzymatic reactions.
authors.affiliation: State Key Laboratory of Brain and Cognitive Sciences, Institute of Biophysics, Chinese Academy of Sciences, 15 Da Tun Road, Chao Yang District, Beijing 100101, China.
authors.forename: Rong
authors.initials: R
authors.lastname: Pan
authors.forename: Image
authors.initials: I
authors.lastname: Image
authors.forename: Xue-Jing
authors.initials: XJ
authors.lastname: Zhang
authors.forename: Image Image
authors.initials: II
authors.lastname: Image
authors.forename: Zi-Jian
authors.initials: ZJ
authors.lastname: Zhang
authors.forename: Image Image
authors.initials: II
authors.lastname: Image
authors.forename: Yuan
authors.initials: Y
authors.lastname: Zhou
authors.forename: Image
authors.initials: I
authors.lastname: Image
authors.forename: Wei-Xi
authors.initials: WX
authors.lastname: Tian
authors.forename: Image Image
authors.initials: II
authors.lastname: Image
authors.forename: Rong-Qiao
authors.initials: RQ
authors.lastname: He
authors.forename: Image Image
authors.initials: II
authors.lastname: Image
mesh_terms: D000818:Animals; D020134:Catalytic Domain / Q000187:drug effects*; D009835:Oligochaeta / Q000201:enzymology*; D009842:Oligopeptides / Q000378:metabolism / Q000494:pharmacology; D010447:Peptide Hydrolases / Q000737:chemistry* / Q000378:metabolism*; D013379:Substrate Specificity
chemical_list: D009842:Oligopeptides; C053661:chromozym U; C014413:chromozym TH; D010447:Peptide Hydrolases