Koga H, Yamada H, Nishimura Y, Kato K, Imoto T
Faculty of Pharmaceutical Sciences, Kyushu University 62, Fukuoka.
J Biochem. 1990 Dec;108(6):976-82. doi: 10.1093/oxfordjournals.jbchem.a123324.
Sixty-nine rat cathepsin L-susceptible peptide bonds were analyzed employing various peptide substrates. The proteolytic specificities of rat cathepsin L and papain were compared and the results are discussed in relation to differences in amino acid residues around their binding sites. The specificity of cathepsin L, which is characterized by a remarkable preference for hydrophobic amino acids at the P2 site of the scissile peptide bonds, was analogous to that of papain as a whole. This analogous specificity suggests that the binding sites of the two proteases are analogous, as expected from their homologous amino acid sequences. However, there is a slight difference in the preference for S3 site between them. That is, cathepsin L showed a greater preference for bulky and hydrophobic amino acids at the S3 site than did papain. Based on the computer-graphically deduced structure of the binding sites of cathepsin L, the preferences for hydrophobic amino acids at the S2 site and for bulky and hydrophobic amino acids at the S3 site of the protease are supposed to be related to the compensating amino acid substitutions at the S2 site (V133A and V157L) and the reduction in size at the S3 site (Y61Q and Y67L), respectively. The discussion of the effect of the amino acid substitutions on the proteolytic activities of cathepsin L and papain in this paper provides a basis for more advanced studies of the relationship between structure and function of proteases belonging to the papain superfamily by means of protein engineering.
利用各种肽底物分析了69个大鼠组织蛋白酶L敏感的肽键。比较了大鼠组织蛋白酶L和木瓜蛋白酶的蛋白水解特异性，并结合它们结合位点周围氨基酸残基的差异对结果进行了讨论。组织蛋白酶L的特异性表现为对可裂解肽键P2位点的疏水氨基酸有显著偏好，总体上与木瓜蛋白酶类似。这种类似的特异性表明这两种蛋白酶的结合位点类似，正如从它们同源的氨基酸序列所预期的那样。然而，它们对S3位点的偏好略有不同。也就是说，与木瓜蛋白酶相比，组织蛋白酶L对S3位点的大体积疏水氨基酸表现出更强的偏好。基于计算机图形推导的组织蛋白酶L结合位点结构，蛋白酶S2位点对疏水氨基酸的偏好以及S3位点对大体积疏水氨基酸的偏好分别被认为与S2位点的补偿性氨基酸取代（V133A和V157L）以及S3位点的尺寸减小（Y61Q和Y67L）有关。本文对氨基酸取代对组织蛋白酶L和木瓜蛋白酶蛋白水解活性影响的讨论为通过蛋白质工程更深入研究木瓜蛋白酶超家族蛋白酶的结构与功能关系提供了基础。
