One ,β Hairpin Follows the Other: Exploring Refolding Pathways and Kinetics of the Transmembrane β-Barrel Protein OmpG

摘要

Despite their enormous relevance to cellular vitality, the folding mechanisms of only a few transmembrane proteins have been studied. From these studies, only a handful of β-stranded membrane proteins were characterized. Current models describe that transmembrane β barrels fold into the lipid membrane in two major steps. Firstly, the unfolded polypeptide interacts with the lipid surface where it folds, tilts, and then inserts into the membrane. Consequently, it is thought that single β strands and β hairpins form unstable units, and that β-barrel proteins (pre-)fold prior to their insertion into the cellular membrane. Experiments studying the (un-)folding of membrane proteins are conventionally carried out by using thermal or chemical denaturation. In most cases, membrane proteins that were solubilized in detergent and/or exposed to approximately 4-10 m urea were studied. In vivo membrane proteins fold under different conditions. Thus, the folding pathways studied may be different from those that occur in nature.