G. Pal et al., STABLE MONOMERIC FORM OF AN ORIGINALLY DIMERIC SERINE PROTEINASE-INHIBITOR, ECOTIN, WAS CONSTRUCTED VIA SITE-DIRECTED MUTAGENESIS, FEBS letters, 385(3), 1996, pp. 165-170
Ecotin, a homodimer protein of E. coli, is a unique member of canonica
l serine proteinase inhibitors, since it is a potent agent against a v
ariety of serine proteinases having different substrate specificity, M
onomers of ecotin are held together mostly by their long C-terminal st
rands that are arranged as a two-stranded antiparallel beta-sheet in t
he functional dimer, One ecotin dimer can chelate two proteinase molec
ules, each of them bound to both subunits of ecotin at two different s
ites, namely the specific primary and the non-specific secondary bindi
ng sites, In this study the genes of wild type ecotin and its Met(84)A
rg 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 assem
ble into the familiar heterotetramer, Our data suggest that this heter
otetramer exists even in extremely diluted solutions, and the interact
ion, which is responsible for the dimerization of ecotin, contributes
to the stability of the heterotetrameric complex.