Booth Rachell E, Lovell Simon C, Misquitta Stephanie A, Bateman Robert C
Department of Chemistry and Biochemistry, Texas State University-San Marcos, San Marcos, TX 78666, USA.
BMC Biol. 2004 Feb 10;2:2. doi: 10.1186/1741-7007-2-2.
Glutaminyl cyclase (QC) forms the pyroglutamyl residue at the amino terminus of numerous secretory peptides and proteins. We previously proposed the mammalian QC has some features in common with zinc aminopeptidases. We now have generated a structural model for human QC based on the aminopeptidase fold (pdb code 1AMP) and mutated the apparent active site residues to assess their role in QC catalysis.
The structural model proposed here for human QC, deposited in the protein databank as 1MOI, is supported by a variety of fold prediction programs, by the circular dichroism spectrum, and by the presence of the disulfide. Mutagenesis of the six active site residues present in both 1AMP and QC reveal essential roles for the two histidines (140 and 330, QC numbering) and the two glutamates (201 and 202), while the two aspartates (159 and 248) appear to play no catalytic role. ICP-MS analysis shows less than stoichiometric zinc (0.3:1) in the purified enzyme.
We conclude that human pituitary glutaminyl cyclase and bacterial zinc aminopeptidase share a common fold and active site residues. In contrast to the aminopeptidase, however, QC does not appear to require zinc for enzymatic activity.
谷氨酰胺环化酶（QC）在众多分泌肽和蛋白质的氨基末端形成焦谷氨酰残基。我们之前提出哺乳动物的QC与锌氨肽酶有一些共同特征。现在我们基于氨肽酶折叠（pdb代码1AMP）生成了人QC的结构模型，并对明显的活性位点残基进行了突变，以评估它们在QC催化中的作用。
这里提出的人QC结构模型（存入蛋白质数据库为1MOI）得到了各种折叠预测程序、圆二色光谱以及二硫键存在情况的支持。对1AMP和QC中存在的六个活性位点残基进行诱变，发现两个组氨酸（140和330，QC编号）和两个谷氨酸（201和202）起着关键作用，而两个天冬氨酸（159和248）似乎没有催化作用。电感耦合等离子体质谱分析表明，纯化的酶中锌含量低于化学计量比（0.3:1）。
我们得出结论，人垂体谷氨酰胺环化酶和细菌锌氨肽酶具有共同的折叠和活性位点残基。然而，与氨肽酶不同的是，QC的酶活性似乎不需要锌。
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