Abstract
Secretion systems are employed by bacteria to transport macromolecules across membranes without compromising their integrities. Processes including virulence, colonization, and motility are highly dependent on the secretion of effector molecules toward the immediate cellular environment, and in some cases, into the host cytoplasm. In Type II and Type III secretion systems, as well as in Type IV pili, homomultimeric complexes known as secretins form large pores in the outer bacterial membrane, and the localization and assembly of such 1 MDa molecules often relies on pilotins or accessory proteins. Significant progress has been made toward understanding details of interactions between secretins and their partner proteins using approaches ranging from bacterial genetics to cryo electron microscopy. This review provides an overview of the mode of action of pilotins and accessory proteins for T2SS, T3SS, and T4PS secretins, highlighting recent near-atomic resolution cryo-EM secretin complex structures and underlining the importance of these interactions for secretin functionality.
Highlights
Bacteria depend on the transport of molecules, toxins, and macromolecules to the external environment in order to survive and proliferate
It was later identified that PA3611, a conserved T2SS protein of unknown function in P. aeruginosa, presents high structural similarity to AspS, and has no lipoprotein signature sequence.[38]
This observation led authors to suggest that the function of PA3611 could involve recognition of the S-domain of its cognate secretin HxcQ but could be limited to protecting it from proteolysis, which is plausible in the case of an autopiloting secretin like HxcQ
Summary
Bacteria depend on the transport of molecules, toxins, and macromolecules to (and from) the external environment in order to survive and proliferate.
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