Elucidation of the Mechanisms of Induced-fit Movement imposed on Enzymes and Substrates as studied by Precise Crystal Structure Analysis.

关于一种微生物蛋白酶“Subtilisin”及其底物（实际上是蛋白质抑制剂）“SSI”（Streptomyces Subtilisin inhibitor），已经实现或阐明了以下内容。1)游离SSI晶体结构分析的分辨率从2.6 <ang>提高到1.85 <ang>。2) SSI-Subtilisin配合物的晶体结构分析分辨率从2.6 <ang>提高到2.0 <ang>。3)利用1)和2)的结果，分析了枯草菌素酶和底物SSI在络合物形成时的构象变化的详细性质。在此分析中，充分利用了新设计的“差距图”和“相对差距图”。3A)在与底物SSI形成复合物后，枯草杆菌酶的整体结构几乎没有变化，尽管确实发生了一些局部的诱导拟合运动。3B)底物SSI在与枯草杆菌酶以如下所述的方式形成复合物后发生全局构象变化。a)由10个连续的氨基酸残基组成的任何局部结构内没有明显的构象变化，b) < α > -螺旋本身没有发生任何明显的构象变化，c)任何两个相邻的< β > -链的相对配置没有明显变化，d) < α _1> -螺旋与< β _1> -和< β _2> -链相隔约2 <ang>。3C)上述3B)中描述的构象变化机理，与“铰链弯曲机制”和“螺旋剪切机制”这两种众所周知的机制相比，是独特的。

Regarding a microbial proteinase "Subtilisin" and its substrate (actually proteinaceous inhibitor) "SSI"(Streptomyces Subtilisin Inhibitor), the followings have been achieved or elucidated.1) Resolution of the crystal structure analysis of free SSI was raised to 1.85 <ang> (from 2.6 <ang> ).2) Resolution of the crystal structure analysis of SSI-Subtilisin complex was raised to 2.0 <ang> (from 2.6 <ang> ).3) Making use of the results of 1) and 2), the detailed nature of the conformational change imposed on the enzyme Subtilisin and the substrate SSI upon complex formation was analyzed. For this analysis, the newly devised "Difference Distance Map" and the "Relative Difference Distance Map" were fully made use of. 3A) The global structure of the enzyme Subtilisin is virtually unchanged after complex formation with the substrate SSI, although some local induced-fit movement does occur. 3B) The substrate SSI undergoes global conformational change upon complex formation with the enzyme Subtilisin in the way described below. a) No conspicuous conformational changes occur within any local structure formed by 10 consecutive amino acid residues, b) no <alpha> -helices per se undergoes any significant conformational change, c) no conspicuous changes occur in the relative disposition of any two neighbouring <beta> -strands, d) the <alpha_1> -helix is separated from the <beta_1> - and <beta_2> -strands by ca. 2 <ang> . 3C) The mechanism of conformational change described in 3B) above is unique in the light of the two well-known mechanisms, the "hinge bending mechanism" and the "helix shear mechanism".