Detergent headgroups control TolC folding in vitro

TolC is the trimeric outer membrane component of the efflux pump system in E. coli responsible for antibiotic efflux from bacterial cells. Over-expression of efflux pumps has been reported to decrease susceptibility to antibiotics in a variety of bacterial pathogens. Reliable production of membrane proteins allows for the biophysical and structural characterization needed to better understand efflux and for the development of therapeutics. Preparation of recombinant protein for biochemical/structural studies often involves the production of proteins as inclusion body aggregates from which bioactive proteins are recovered. Here we find that the in vitro folding of TolC into its functional trimeric state from inclusion bodies is dependent on the headgroup composition of detergent micelles used. Nonionic detergent favors the formation of functional trimeric TolC, whereas zwitterionic detergents induce the formation of a non-native trimeric TolC fold. We also find that nonionic detergents with shorter alkyl lengths facilitate TolC folding. It remains to be seen whether the charges in lipid headgroups have similar effects on membrane insertion and folding in biological systems.