Abstract
Protein secretion is initiated at the endoplasmic reticulum by the COPII coat, which self-assembles to form vesicles. Here, we examine the mechanisms by which a cargo-bound inner coat layer recruits and is organized by an outer scaffolding layer to drive local assembly of a stable structure rigid enough to enforce membrane curvature. An intrinsically disordered region in the outer coat protein, Sec31, drives binding with an inner coat layer via multiple distinct interfaces, including a newly defined charge-based interaction. These interfaces combinatorially reinforce each other, suggesting coat oligomerization is driven by the cumulative effects of multivalent interactions. The Sec31 disordered region could be replaced by evolutionarily distant sequences, suggesting plasticity in the binding interfaces. Such a multimodal assembly platform provides an explanation for how cells build a powerful yet transient scaffold to direct vesicle traffic.
Highlights
Proteins within the secretory pathway are transported by vesicles activating protein, Sec23, for GTP hydrolysis (Yoshihisa et al, 1993).generated by cytoplasmic coat proteins, which simultaneously Sec31 further accelerates this reaction (Antonny et al, 2001) via a recruit appropriate cargo and sculpt the donor membrane into short “active fragment” that contacts both Sec23 and Sar1
PPP-driven interactions are dispensable for coat assembly but contribute to coat stability We first tested the importance of PPP motifs in COPII assembly by mutagenesis of the Sec23 gelsolin domain that interacts with
When coat assembly is stabilized by inhibiton of GTP hydrolysis, perturbation of the gelsolin-PPP interaction has minimal effect, but under the condition of GTP-dependent coat turnover (Antonny et al, 2001), loss of this interface impairs vesicle formation
Summary
Proteins within the secretory pathway are transported by vesicles activating protein, Sec, for GTP hydrolysis (Yoshihisa et al, 1993). Generated by cytoplasmic coat proteins, which simultaneously Sec further accelerates this reaction (Antonny et al, 2001) via a recruit appropriate cargo and sculpt the donor membrane into short “active fragment” that contacts both Sec and Sar The COPII coat hydrolysis and prolong coat association sufficiently to produce a comprises five proteins that self-assemble on the cytosolic face of vesicle? The presence of cargo proteins prolongs coat associthe ER membrane to traffic nascent secretory proteins toward the ation with the membrane after GTP hydrolysis
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