Thiol-dependent Gelation of the Domain I-truncated Fragment of Bovine Serum Albumin

Abstract

The thiol-dependent gelation of bovine serum albumin (BSA) was compared between the intact form (molecular mass of 66 kDa) and the domain I-truncated fragment (molecular mass of 45 kDa). The hardness of the gel that was induced by incubating with 70 mM 2-mercaptoethanol (2-ME) was the maximum at pH 7.5 for intact BSA, but the maximum was at pH 6.5 for the fragment. The gel hardness was increased with increasing protein concentration in a similar manner for intact BSA and for the BSA fragment, although the BSA fragment had a maximum gel hardness at a lower 2-ME concentration than that for intact BSA. Non-reducing SDS-PAGE revealed that the fomation of intermolecular disulfide bonds was involved in the gelation of both the protein forms. Both the disulfide-reduced form of the fragment and intact BSA were found by CD spectra to assume a molten globule-like state. The β-strand content in this state appears to have been closely correlated with the difference in pH optimum for gelation of the two forms of BSA.