Bruun A W, Svendsen I, Sørensen S O, Kielland-Brandt M C, Winther J R
Department of Yeast Genetics, Carlsberg Laboratory, Copenhagen Valby, Denmark.
Biochemistry. 1998 Mar 10;37(10):3351-7. doi: 10.1021/bi971286w.
A 25-kDa inhibitor of the vacuolar enzyme carboxypeptidase Y from Saccharomyces cerevisiae has been characterized. The inhibitor, Ic, binds tightly with an apparent Ki of 0.1 nM. Consistent with a cytoplasmic localization, Ic is soluble and contains no sequences which could serve as potential signals for transport into the endoplasmic reticulum. Surprisingly, Ic is encoded by TFS1, which has previously been isolated as a high-copy suppressor of cdc25-1. CDC25 encodes the putative GTP exchange factor for Ras1p/Ras2p in yeast. In an attempt to rationalize this finding, we looked for a physiological relationship by deleting or overexpressing the gene for carboxypeptidase Y in a cdc25-1 strain. However, this did not change the phenotype of this mutant strain. Ic is the first member of a new family of protease inhibitors. The inhibitor is not hydrolyzed on binding to CPY. It has fairly high degree of specificity, showing a 200-fold higher Ki toward a carboxypeptidase from Candida albicans which is highly homologous to carboxypeptidase Y. The TFS1 gene product shows extensive similarity to a class of proteins termed "21-23-kDa lipid binding proteins", members of which are found in several higher eukaryotes, including man. These proteins are highly abundant in some tissues (e.g., brain) and have in general been found to bind lipids. Considering their homology to Ic, it is tempting to speculate that they may also be inhibitors of serine carboxypeptidases.
已对来自酿酒酵母的液泡酶羧肽酶Y的一种25 kDa抑制剂进行了表征。该抑制剂Ic紧密结合，表观抑制常数Ki为0.1 nM。与细胞质定位一致，Ic是可溶的，并且不包含可作为转运到内质网的潜在信号的序列。令人惊讶的是，Ic由TFS1编码，TFS1先前已作为cdc25-1的高拷贝抑制子被分离出来。CDC25编码酵母中Ras1p/Ras2p的假定鸟苷酸交换因子。为了合理解释这一发现，我们通过在cdc25-1菌株中缺失或过表达羧肽酶Y的基因来寻找生理关系。然而，这并没有改变该突变菌株的表型。Ic是蛋白酶抑制剂新家族的第一个成员。该抑制剂与羧肽酶Y结合时不会被水解。它具有相当高的特异性程度，对来自白色念珠菌的与羧肽酶Y高度同源的羧肽酶的Ki值高200倍。TFS1基因产物与一类称为“21 - 23 kDa脂质结合蛋白”的蛋白质具有广泛的相似性，在包括人类在内的几种高等真核生物中都发现了这类蛋白质的成员。这些蛋白质在某些组织（如大脑）中高度丰富，并且一般已发现它们能结合脂质。考虑到它们与Ic的同源性，很容易推测它们也可能是丝氨酸羧肽酶的抑制剂。
