Eklund H, Müller-Wille P, Horjales E, Futer O, Holmquist B, Vallee B L, Höög J O, Kaiser R, Jörnvall H
Swedish University of Agricultural Sciences, Biomedical Center, Uppsala, Sweden.
Eur J Biochem. 1990 Oct 24;193(2):303-10. doi: 10.1111/j.1432-1033.1990.tb19337.x.
Conformational models of the three characterized classes of mammalian liver alcohol dehydrogenase were constructed using computer graphics based on the known three-dimensional structure of the E subunit of the horse enzyme (class I) and the primary structures of the three human enzyme classes. This correlates the substrate-binding pockets of the class I subunits (alpha, beta and gamma in the human enzyme) with those of the class II and III subunits (pi and chi, respectively) for three enzymes that differ in substrate specificity, inhibition pattern and many other properties. The substrate-binding sites exhibit pronounced differences in both shape and properties. Comparing human class I subunits with those of class II and III subunits there are no less than 8 and 10 replacements, respectively, out of 11 residues in the substrate pocket, while in the human class I isozyme variants, only 1-3 of these 11 positions differ. A single residue, Val294, is conserved throughout. The liver alcohol dehydrogenases, with different substrate-specificity pockets, resemble the patterns of other enzyme families such as the pancreatic serine proteases. The inner part of the substrate cleft in the class II and III enzymes is smaller than in the horse class I enzyme, because both Ser48 and Phe93 are replaced by larger residues, Thr and Tyr, respectively. In class II, the residues in the substrate pocket are larger in about half of the positions. It is rich in aromatic residues, four Phe and one Tyr, making the substrate site distinctly smaller than in the class I subunits. In class III, the inner part of the substrate cleft is narrow but the outer part considerably wider and more polar than in the class I and II enzymes. In addition, Ser (or Thr) and Tyr in class II and III instead of His51 may influence proton abstraction/donation at the active site.
基于马肝醇脱氢酶E亚基（I类）已知的三维结构以及三种人类酶类的一级结构，利用计算机图形技术构建了三类已明确特征的哺乳动物肝醇脱氢酶的构象模型。这将I类亚基（人类酶中的α、β和γ）的底物结合口袋与II类和III类亚基（分别为π和χ）的底物结合口袋关联起来，这三种酶在底物特异性、抑制模式和许多其他特性方面存在差异。底物结合位点在形状和性质上都表现出明显的差异。将人类I类亚基与II类和III类亚基进行比较，底物口袋中的11个残基分别有不少于8个和10个替换，而在人类I类同工酶变体中，这11个位置中只有1 - 3个不同。有一个残基Val294在所有酶中都保守。具有不同底物特异性口袋的肝醇脱氢酶类似于其他酶家族的模式，如胰腺丝氨酸蛋白酶。II类和III类酶中底物裂隙的内部比马I类酶中的小，因为Ser48和Phe93分别被更大的残基Thr和Tyr取代。在II类中，底物口袋中约一半位置的残基更大。它富含芳香族残基，有四个Phe和一个Tyr，使得底物位点明显小于I类亚基中的底物位点。在III类中，底物裂隙的内部狭窄，但外部比I类和II类酶宽得多且极性更强。此外，II类和III类中的Ser（或Thr）和Tyr取代了His51，可能会影响活性位点处的质子提取/供体作用。
