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Evaluation of Potential Binding Interactions Between the Sec1/Munc18 Family Protein Sly1 and Its Cognate SNAREs
Howells, Sarah C.
Hughson, Frederick M.
Princeton University. Department of Molecular Biology
This Abstract contains text that is based closely on, or identical to, text found in my Junior Paper [Sarah Howells, SM family protein Sly1 Interaction with R-SNAREs in the Anterograde and Retrograde Trafficking Pathways from Endoplasmic Reticulum to Golgi Apparatus, Junior Independent Work Paper, Spring 2015]. Cell trafficking is a process by which cargo-carrying vesicles fuse with target membranes within the cell to release proteins into specific cellular compartments. The Sec1/Munc18 (SM) protein Sly1 chaperones trans-SNARE complex formation to promote vesicle fusion with target membranes. It is well established that Sly1 binds Qa- SNAREs in trafficking pathways from the endoplasmic reticulum (ER) to the Golgi apparatus. Yet the possibility of functionally important interactions between Sly1 and its cognate Qb-SNAREs, Qc-SNARES, and R-SNAREs has not been rigorously explored. Recently, our lab discovered that the SM protein Vps33 binds the R-SNARE Nyv1 in a surface groove homologous to that covered by a “lid” formed by a short helical region, α20, on Sly1. Mutations that destabilize α20 suppress deleterious mutations in trafficking proteins such as vesicle-bound Rab GTPases and some multisubunit tethering complexes, including Dsl1. Using gel filtration binding assays, we determined that wild-type Sly1 and lid mutant Sly1-20 do not bind the SNARE domains of the cognate Qb-SNARE Sec20, Qc-SNARE Use1, and R-SNAREs Sec22 and Ykt6. We also established that Sly1-20 binds the retrograde Qa-SNARE Ufe1, like wild-type Sly1, although Sly1-20 failed to form a ternary complex with the Ufe1 N-peptide and Ykt6. Future work should test ternary complex formation of cytoplasmic Qa-SNAREs and R-SNAREs with Sly1-20 and compete crystallization trials of Sly1-20 with SNAREs. Our results suggest that unlike Vps33, but like the SM protein Munc18, Sly1 initiates SNARE complex formation by interaction with its cognate Qa-SNAREs.
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