Folding studies of purified LamB protein, the maltoporin from the Escherichia coli outer membrane: Trimer dissociation can be separated from unfolding

► Unfolding and refolding LamB protein in detergent exhibits extreme hysteresis. ► Without its disulfide bond, LamB protein unfolds in low denaturant concentrations. ► The disulfide bond clasps the sides of L1 at the inner wall of the β-barrel. ► Low pH dissociates the LamB trimer to folded monomers, observable on SDS PAGE. ► Low pH disrupts salt bridges between L2 of the adjacent subunit and the β- barrel.