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bioRxiv · 10.1101/2020.01.16.909523

PE5-PPE4-EspG3 trimer structure from mycobacterial ESX-3 secretion system gives insight into cognate substrate recognition by ESX systems

Williamson, Z. A.·Chaton, C. T.·Ciocca, W. A.·Korotkova, N.·Korotkov, K. V.
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Abstract

Mycobacterium tuberculosis (Mtb) has evolved numerous type VII secretion (ESX) systems to secrete multiple factors important for both growth and virulence across their cell envelope. Three such systems; ESX-1, ESX-3, and ESX-5; have been shown to each secrete a unique set of substrates. A large class of these substrates secreted by these three systems are the PE and PPE families of proteins. Proper secretion of the PE-PPE proteins requires the presence of EspG, with each system encoding its own unique copy. There is no cross-talk between any of the ESX systems and how each EspG is recognizing its subset of PE-PPE proteins is currently unknown. The only current structural characterization of PE-PPE-EspG trimers is from the ESX-5 system. Here we present the crystal structure of the PE5mt-PPE4mt-EspG3mm trimer, from the ESX-3 system. Our trimer reveals that EspG3mm interacts exclusively with PPE4mt in a similar manner to EspG5, shielding the hydrophobic tip of PPE4mt from solvent. The C-terminal helical domain of EspG3mm is dynamic, alternating between an open and closed form, and this movement is likely functionally relevant in the unloading of PE-PPE heterodimers at the secretion machinery. In contrast to the previously solved ESX-5 trimers, the PE-PPE heterodimer of our ESX-3 trimer is interacting with its chaperone at a drastically different angle, and presents different faces of the PPE protein to the chaperone. We conclude that the PPE-EspG interface from each ESX system has a unique shape complementarity that allows each EspG to discriminate amongst non-cognate PE-PPE pairs.

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Williamson, Z. A., Chaton, C. T., Ciocca, W. A., Korotkova, N., Korotkov, K. V.. 2020-01-17. PE5-PPE4-EspG3 trimer structure from mycobacterial ESX-3 secretion system gives insight into cognate substrate recognition by ESX systems. https://doi.org/10.1101/2020.01.16.909523

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