Structure, Dynamics and Activity of Bacterial Secretosome

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Bacteria secrete proteins for a wide range of activities, including envelope biogenesis, pathogenicity and degradation of antibiotics. The major export route is via the ubiquitous Sec translocon. This proposal concerns the mechanism of this process and subsequent poorly understood downstream transit through the bacterial envelope.

The Gram-negative envelope is composed of an inner- and outer-membrane; sandwiched between them is the periplasm incorporating a peptidoglycan (PG) layer. The mechanism of transport across the inner-membrane is relatively well understood. However, it is unclear how they are then rapidly and specifically sorted into the periplasm, or delivery to the outer-membrane-all done in the absence of energy.

We have identified interactions between the holo-translocon (HTL), periplasmic chaperones and the beta-barrel assembly machinery (BAM), forming a super structure spanning the entirety of the envelope. This assembly-the secretosome-could form a contiguous conduit for efficient and quality controlled passage of proteins to the outer-membrane. Its existence has far reaching implications for our understanding of envelope biogenesis.

Our exploration of this unexpected aspect of bacterial biology will harness complementary expertise in biochemistry and cryo-EM at Bristol, combined with recent technological advances for hydrogen deuterium exchange mass spectrometry (HDX-MS), with cyclic ion mobility for enhanced resolution, in Manchester. This powerful combination will enable an interrogation of the activity, structure and dynamics of the secretosome-leading to greater knowledge of the molecular mechanisms underlying protein transport across the inner-membrane and through the envelope. The project will enlighten our understanding of a fundamental process, essential for survival. Moreover, the results will suggest strategies to subvert the process of envelope biogenesis and maintenance, and thereby help towards the development new antibiotics.