Pál G, Szilágyi L, Gráf L
Department of Biochemistry, Eötvös University, Budapest, Hungary.
FEBS Lett. 1996 May 6;385(3):165-70. doi: 10.1016/0014-5793(96)00376-6.
Ecotin, a homodimer protein of E. coli, is a unique member of canonical serine proteinase inhibitors, since it is a potent agent against a variety of serine proteinases having different substrate specificity. Monomers of ecotin are held together mostly by their long C-terminal strands that are arranged as a two-stranded antiparallel beta-sheet in the functional dimer. One ecotin dimer can chelate two proteinase molecules, each of them bound to both subunits of ecotin at two different sites, namely the specific primary and the non-specific secondary binding sites. In this study the genes of wild type ecotin and its Met84Arg P1 site mutant were truncated resulting in new forms of ecotin that lack 10 amino acid residues at their C-terminus. These mutants do not dimerize spontaneously, though in combination with trypsin they assemble into the familiar heterotetramer. Our data suggest that this heterotetramer exists even in extremely diluted solutions, and the interaction, which is responsible for the dimerization of ecotin, contributes to the stability of the heterotetrameric complex.
埃科汀是大肠杆菌的一种同二聚体蛋白，是典型丝氨酸蛋白酶抑制剂中的独特成员，因为它是针对多种具有不同底物特异性的丝氨酸蛋白酶的强效试剂。埃科汀单体主要通过其长的C末端链结合在一起，这些链在功能性二聚体中排列成两条链的反平行β-折叠。一个埃科汀二聚体可以螯合两个蛋白酶分子，每个蛋白酶分子在两个不同位点与埃科汀的两个亚基结合，即特异性的一级结合位点和非特异性的二级结合位点。在本研究中，野生型埃科汀及其Met84Arg P1位点突变体的基因被截短，产生了新形式的埃科汀，其C末端缺少10个氨基酸残基。这些突变体不会自发二聚化，不过与胰蛋白酶结合时它们会组装成常见的异源四聚体。我们的数据表明，这种异源四聚体即使在极稀溶液中也存在，并且负责埃科汀二聚化的相互作用有助于异源四聚体复合物的稳定性。
