Tate S S, Khadse V, Wellner D
Department of Biochemistry, Cornell University Medical College, New York, New York 10021.
Arch Biochem Biophys. 1988 May 1;262(2):397-408. doi: 10.1016/0003-9861(88)90390-6.
Mammalian kidney gamma-glutamyl transpeptidases are compared with respect to subunit size, amino-terminal sequences of the two subunits, immunological, and some catalytic properties. The species-related variation in the apparent molecular weight of the subunits has been shown to be primarily due to the extent and nature of protein glycosylation. Using antibodies raised against the native enzymes and isolated sodium dodecyl sulfate-treated subunits, it is shown that the transpeptidases share some antigenic determinants. Some of these determinants in the highly glycosylated transpeptidase subunits can be detected by the antibodies only upon deglycosylation of the subunits. The amino-terminal sequences of the subunits exhibit considerable homology, in agreement with the immunological data. Thus, there are two segments of identity (3 and 5 residues in length, respectively) in the first 17 amino-terminal residues of the heavy subunits of rat, bovine, dog, and human kidney transpeptidases (papain-solubilized). Of particular interest is the finding of 91 to 96% identity in the first 23 amino-terminal residues of the small subunit of these transpeptidases. The small subunit contains the gamma-glutamyl binding site of the enzyme. There are three segments of identity (7, 6, and 8 residues in length, respectively) in the first 23 residues, each separated by either a Ser or an Ala residue. The first 7 amino-terminal residues of the small subunit in all four species are identical, indicating a high degree of specificity in the proteolytic processing of the common, single-chain precursor of the two subunits. Differences noted between transpeptidases in their relative acceptor specificity and in their susceptibility to inactivation by the glutamine antagonist, AT-125 (acivicin), must reflect subtle structural differences in their active center domains.
对哺乳动物肾脏γ-谷氨酰转肽酶的亚基大小、两个亚基的氨基末端序列、免疫学特性及一些催化特性进行了比较。已表明亚基表观分子量的物种相关变异主要归因于蛋白质糖基化的程度和性质。使用针对天然酶和分离的经十二烷基硫酸钠处理的亚基产生的抗体，结果表明转肽酶具有一些共同的抗原决定簇。只有在亚基去糖基化后，这些抗体才能检测到高度糖基化的转肽酶亚基中的一些决定簇。亚基的氨基末端序列表现出相当程度的同源性，这与免疫学数据一致。因此，大鼠、牛、狗和人肾脏转肽酶（木瓜蛋白酶可溶解的）重亚基的前17个氨基末端残基中有两个相同片段（分别为3个和5个残基长度）。特别有趣的是，这些转肽酶小亚基的前23个氨基末端残基中有91%至96%的同源性。小亚基包含该酶的γ-谷氨酰结合位点。在前23个残基中有三个相同片段（分别为7个、6个和8个残基长度），每个片段之间由一个丝氨酸或丙氨酸残基隔开。所有四个物种中小亚基的前7个氨基末端残基相同，这表明在两个亚基的共同单链前体的蛋白水解加工过程中具有高度特异性。转肽酶在其相对受体特异性以及对谷氨酰胺拮抗剂AT-125（阿西维辛）失活的敏感性方面存在的差异，必定反映了它们活性中心结构域中的细微结构差异。
