Exomer is a cargo adaptor that mediates the sorting of specific plasma membrane proteins into vesicles at the trans-Golgi network. Cargo adaptors must bind to multiple partners, including their cargo, regulatory proteins, and the membrane surface. During biogenesis of a vesicle, the membrane makes a transition from a relatively flat surface to one of high curvature, requiring cargo adaptors to somehow maintain protein-protein and protein-membrane interactions on a changing membrane environment. Here, we present the crystal structure of a tetrameric Chs5/Bch1 exomer complex and use small-angle X-ray scattering to demonstrate its flexibility in solution. The structural data suggest that the complex flexes primarily around the dimeric N-terminal domain of the Chs5 subunits, which adopts a noncanonical β sandwich fold. We propose that this flexible hinge domain enables exomer to maintain interactions in the context of a dynamic membrane environment.
Bibliographical noteFunding Information:
We gratefully acknowledge the assistance and advice of CHESS A1 and F2 beamline staff, especially that of Richard Gillilan with respect to SAXS data collection and analysis. We thank Holger Sondermann for helpful discussion regarding NMA; Julia Kumpf for Chs5/Bud7 complex purification; Mike Henne for critical reading of the manuscript; and Jon Paczkowski for assistance with X-ray data collection, Chs5/Chs6 complex purification, and critical reading of the manuscript. This work is based upon research conducted at CHESS, which is supported by the National Science Foundation and the National Institutes of Health/National Institute of General Medical Sciences under NSF award DMR-0936384, using the Macromolecular Diffraction at CHESS (MacCHESS) facility, which is supported by award GM103485 from the National Institutes of Health, through its National Institute of General Medical Sciences. This work was funded by Cornell University startup funds.