The Sec1/Munc18 Protein Groove Plays a Conserved Role in Interaction with Sec9p/SNAP‐25

• Published in: Traffic (Copenhagen, Denmark) Denmark), 2016-02, Vol.17 (2), p.131-153
• Main Authors: Weber‐Boyvat, Marion, Chernov, Konstantin G., Aro, Nina, Wohlfahrt, Gerd, Olkkonen, Vesa M., Jäntti, Jussi
• Format: Article
• Language: English
• Subjects: Animals; Cell Line; Cell Membrane - metabolism; exocytosis; Fungal Proteins - genetics; Fungal Proteins - metabolism; Humans; Membrane Fusion - physiology; Munc18; Munc18 Proteins - genetics; Munc18 Proteins - metabolism; Mutation - genetics; Protein Binding - physiology; Proteins; Sec1; Sec9; SNAP‐25; SNARE; Sro7; Synaptosomal-Associated Protein 25 - genetics; Synaptosomal-Associated Protein 25 - metabolism; Tomosyn; Yeasts - genetics; Yeasts - metabolism
• ISSN: 1398-9219; 1600-0854
• DOI: 10.1111/tra.12349

The events orchestrating vesicle targeting and fusion at the plasma membrane are poorly understood. The Sec1/Munc18 proteins have an essential role in SNARE‐mediated membrane fusion. We show in yeast and mammalian cells that ‘the groove’, a recently identified protein interaction site in Sec1p, plays an important role in mediating interactions with Sec9p/SNAP‐25. ‘The groove’ represents an evolutionarily conserved site for Sec9p/SNAP‐25 binding and plays, in concert with Sro7p, a regulatory role in initial steps of exocytic SNARE complex assembly. The Sec1/Munc18 (SM) proteins constitute a conserved family with essential functions in SNARE‐mediated membrane fusion. Recently, a new protein–protein interaction site in Sec1p, designated the groove, was proposed. Here, we show that a sec1 groove mutant yeast strain, sec1(w24), displays temperature‐sensitive growth and secretion defects. The yeast Sec1p and mammalian Munc18‐1 grooves were shown to play an important role in the interaction with the SNAREs Sec9p and SNAP‐25b, respectively. Incubation of SNAP‐25b with the Munc18‐1 groove mutant resulted in a lag in the kinetics of SNARE complex assembly in vitro when compared with wild‐type Munc18‐1. The SNARE regulator SRO7 was identified as a multicopy suppressor of sec1(w24) groove mutant and an intact Sec1p groove was required for the plasma membrane targeting of Sro7p–SNARE complexes. Simultaneous inactivation of Sec1p groove and SRO7 resulted in reduced levels of exocytic SNARE complexes. Our results identify the groove as a conserved interaction surface in SM proteins. The results indicate that this structural element is important for interactions with Sec9p/SNAP‐25 and participates, in concert with Sro7p, in the initial steps of SNARE complex assembly.