title: p115-SNARE interactions: a dynamic cycle of p115 binding monomeric SNARE motifs and releasing assembled bundles.
abstract: Tethering factors regulate the targeting of membrane-enclosed vesicles under the control of Rab GTPases. p115, a golgin family tether, has been shown to participate in multiple stages of ER/Golgi transport. Despite extensive study, the mechanism of action of p115 is poorly understood. SNARE proteins make up the machinery for membrane fusion, and strong evidence shows that function of p115 is directly linked to its interaction with SNAREs. Using a gel filtration binding assay, we have demonstrated that in solution p115 stably interacts with ER/Golgi SNAREs rbet1 and sec22b, but not membrin and syntaxin 5. These binding preferences stemmed from selectivity of p115 for monomeric SNARE motifs as opposed to SNARE oligomers. Soluble monomeric rbet1 can compete off p115 from coat protein II (COPII) vesicles. Furthermore, excess p115 inhibits p115 function in trafficking. We conclude that monomeric SNAREs are a major binding site for p115 on COPII vesicles, and that p115 dissociates from its SNARE partners upon SNAREpin assembly. Our results suggest a model in which p115 forms a mixed p115/SNARE helix bundle with a monomeric SNARE, facilitates the binding activity and/or concentration of the SNARE at prefusion sites and is subsequently ejected as SNARE complex formation and fusion proceed.
authors.affiliation: Division of Biological Sciences and Center for Structural & Functional Neuroscience, The University of Montana, Missoula, MT, USA.
authors.forename: Ting
authors.initials: T
authors.lastname: Wang
authors.forename: Robert
authors.initials: R
authors.lastname: Grabski
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Sztul
authors.forename: Jesse C
authors.initials: JC
authors.lastname: Hay
mesh_terms: D000818:Animals; D001665:Binding Sites; D016466:CHO Cells; D022181:COP-Coated Vesicles / Q000378:metabolism; D006224:Cricetinae; D003412:Cricetulus; D000077614:Golgi Matrix Proteins; D011485:Protein Binding; D055503:Protein Multimerization; D021381:Protein Transport; D050767:Qc-SNARE Proteins / Q000737:chemistry / Q000378:metabolism*; D050683:R-SNARE Proteins / Q000737:chemistry / Q000378:metabolism*; D051381:Rats; D033921:Vesicular Transport Proteins / Q000378:metabolism*
chemical_list: C098783:BET1 protein, rat; D000077614:Golgi Matrix Proteins; D050767:Qc-SNARE Proteins; D050683:R-SNARE Proteins; C098784:Sec22a protein, rat; D033921:Vesicular Transport Proteins; C091580:vesicular transport factor p115
keywords: SNARE; bet1; endoplasmic reticulum to Golgi transport; membrane fusion; membrane tethers; p115; sec22; secretion; syntaxin 5; vesicle transport