Bacterial protein secretion through the translocase nanomachine

Abstract

All cells must traffic proteins across their membranes. This essential process is responsible for the biogenesis of membranes and cell walls, motility and nutrient scavenging and uptake, and is also involved in pathogenesis and symbiosis. The translocase is an impressively dynamic nanomachine that is the central component which catalyses transmembrane crossing. This complex, multi-stage reaction involves a cascade of inter- and intramolecular interactions that select, sort and target polypeptides to the membrane, and use energy to promote the movement of these polypeptides across--or their lateral escape and integration into--the phospholipid bilayer, with high fidelity and efficiency. Here, we review the most recent data on the structure and function of the translocase nanomachine.

SecB-like chaperone controls a toxin–antitoxin stress-responsive system in Mycobacterium tuberculosis

“…SecB specifically interacts with the SecA motor component of the Sec translocon at the cytoplasmic membrane (10). Such a unique and dedicated partnership between substrate-bound SecB and SecA facilitates efficient preprotein targeting and transfer to the Sec translocon as well as the subsequent translocation through the membrane (11). As a chaperone with generic properties, SecB also binds aggregation-sensitive cytosolic protein substrates and prevents their aggregation in the absence of the cytosolic chaperones DnaK and Trigger Factor (TF) (12).…”

In vitro evolution of α-hemolysin using a liposome display

“…By adding phospholipids in the form of a unilamellar vesicle whose size is typically 30-200 nm to the IVT, a number of membrane proteins have been shown to be integrated into the membrane from the outside of the vesicle (24). Living cells use translocases to integrate membrane proteins into the lipid bilayer (26,33). For the IVT synthesis of several membrane proteins, the efficiency of membrane insertion has been reported to increase significantly with the translocases (34,35).…”

“…For example, a reporter system, the HaloTag system in our case, can be encapsulated inside the GUVs to detect the activity of the target membrane protein, thereby directly detecting the influx or efflux of particular substances. We can also add other systems, such as membrane translocase (26), when needed. iv) Because the PURE system is composed only of the components involved in protein synthesis, no membrane proteins other than the target protein are present.…”

NMR reveals novel mechanisms of protein activity regulation

“…4(A)]. 102 The size and complexity of the system rendered assignment of the methyl groups of SecA a particularly daunting task. A domain-parsing strategy was followed to assign the methyl groups (Ile, Leu, Met, and Val) with virtually all domains of SecA and a number of fragments comprising contiguous domains being isolated and characterized by NMR.…”