Protein transport is a fundamental activity for all living cells and an exciting area for scientific exploration (1, 2). In bacteria, the process depends on the concerted action of at least three membrane-embedded components: the ubiquitous SecYEG complex that forms the polypeptide-conducting membrane pore, the essential YidC insertase that works independently or in cooperation with SecYEG to insert hydrophobic protein segments into the lipid bilayer, and the auxiliary SecDF–yajC complex that associates with both SecYEG and YidC to accelerate the overall process. Depending on specific requirements of the substrate to be transported, SecYEG also associates with the ribosome or the cytosolic ATPase SecA, which mediate the cotranslational and posttranslational mode of translocation, respectively. Over the last decade, our understanding of the bacterial protein transport process has greatly advanced with the determination of structures for almost all of the individual components (3–5). However, our understanding of the interconnection between these components is still limited because the interactions are weak or transient, and certainly difficult to analyze because they occur in the membrane environment. In PNAS, Schulze et al. (6) report the isolation of a supercomplex that contains all seven subunits: the SecYEG–DFyajC– YidC holo-enzyme aka holo-translocon (HTL). This large membrane assembly of ～250 kDa encompasses 34 transmembrane segments with three large loops exposed on the trans-side of the membrane. The isolation of theHTL is a breakthrough in the field, opening new avenues for investigation; it is also an elegant method that resolves major challenges in membrane biochemistry: membrane complex production and purification.
展开▼
Department of Biochemistry and Molecular Biology, Life Sciences Institute, Faculty of Medicine, University of British Columbia, Vancouver, BC, Canada V6T 1Z3;
