Exploring the Structural and Biochemical Characteristics of the SM Protein Sly1 in Complex with Associated Qa-SNARES Ufe1 and Sed5

Abstract

Vesicular trafficking is controlled by the precise interaction of Rab proteins (G-proteins) and the cell cytoskeleton to deliver important material into and out of the cell and cell organelles. The focus of this paper is the very last step in the process; vesicle and target membrane fusion. This process is carried out by soluble N‑ethylmaleimide sensitive factor attachment protein receptors (SNAREs) which are the necessary and sufficient machinery for inducing membrane fusion. Although SNAREs are sufficient for this process, it occurs at a slow rate. Cells utilize proteins called Sec1/Munc18-like proteins that expedite this process by speeding up SNARE complex formation. Relatively few structures are available that inform us on how SM proteins bind with and transform SNAREs. For the SM protein Sly1, the only published crystal structure is a complex containing a small N-terminal peptide derived from the Qa-SNARE Sed5. This study sought to produce a structure of the Sly1-Sed5 complex containing a more complete Sed5, as well as a structure of Sly1 in complex with a similar SNARE protein named Ufe1. These structures will provide insight into the mechanism(s) whereby SM proteins regulate SNARE assembly.