The CusBAC heavy metal efflux pump of Escherichia coli consists of three essential components spanning the inner membrane, periplasmic space, and outer membrane. The periplasmic adaptor protein CusB connects the inner membrane transporter CusA to the outer membrane factor CusC. The structural studies revealed that the periplasmic component CusB has a unique structure in the CusC interaction region. Recent advances in cryo-electron microscopy have revealed the intermeshing cogwheel interaction between the periplasmic adaptor protein and the outer membrane factor in other types of tripartite efflux pumps, such as AcrAB-TolC and MacAB-TolC. In this study, we built a model of the full complex of the CusBAC pump, where the inner α-helices in CusB are twisted inward to make a similar cogwheel structure to that of AcrA. Binding assay results support the finding that the CusB and CusC binding mode is shared with AcrA and TolC in AcrAB-TolC. Our results give structural insight into a common mechanism for how to seal these proteins to prevent leaks in tripartite efflux pumps.
INTRODUCTION
RESULTS AND DISCUSSION
METHODS