Salt-Induced Changes in the Subunit Structure of the Bacillus stearothermophilus Lipoate Acetyltransferase

The Bacillus stearothermophilus lipoate acetyltransferase (E2), composed of sixty identical, subunits is the core component of the pyruvate dehydrogenase complex (PDC). E2 polypeptide is composed of LD, PSBD, and CD domains. Most studies had focused on a truncated E2 that is deficient in LD and PSBD, because CD mainly contributes to maintaining the multimeric structure. We examined salt-induced changes in E2 without truncation and constructed reaction models. We speculate that in the presence of KCl, E2 is dissociated into a monomer and then assembled into an aggregative complex (C_A) and a quasi-stable complex (C_Q). C_A was larger than C_Q, but smaller than intact E2. C_A and C_Q were dominant complexes at about neutral pH and at basic pH respectively. PDC, in which PSBD is occupied by other components, and a truncated E2 undergo dissociation only. LD-PSBD region besides CD might then contribute to the partial association of dissociated E2.