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bioRxiv · 10.1101/2020.10.08.332312

Structure and mechanism of TRAPPIII-mediated Rab1 activation

Joiner, A. M. N.·Phillips, B. P.·Yugandhar, K.·Sanford, E. J.·Smolka, M. B.·Yu, H.·Miller, E. A.·Fromme, J. C.
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Abstract

The GTPase Rab1 is a master regulator of both the early secretory pathway and autophagy. Rab1 activation is controlled by its GEF (guanine nucleotide exchange factor), the multi-subunit TRAPPIII complex. The Trs85 regulatory subunit is critical for robust activation of Rab1 but its mechanistic role within the complex has remained unclear. Here we report the cryo-EM structure of the intact yeast TRAPPIII complex bound to its substrate Rab1/Ypt1. The orientation of the Rab1/Ypt1 hypervariable domain when bound to the complex leads to a model for how TRAPPIII associates with and activates Rab1/Ypt1 at the membrane surface. We identify a conserved amphipathic -helix motif within Trs85 and demonstrate that this helix is required for stable membrane binding and Rab1/Ypt1 activation by TRAPPIII. Taken together, our results provide a comprehensive analysis of the structure and function of the yeast TRAPPIII complex and reveal that the key function of Trs85 is to serve as a membrane anchor, via its amphipathic helix, for the entire TRAPPIII complex.

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Joiner, A. M. N., Phillips, B. P., Yugandhar, K., Sanford, E. J., Smolka, M. B., Yu, H., Miller, E. A., Fromme, J. C.. 2020-10-08. Structure and mechanism of TRAPPIII-mediated Rab1 activation. https://doi.org/10.1101/2020.10.08.332312

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