Mutations of the SM protein Sly1 resulting in bypass of GTPase requirement in vesicular transport are confined to a short helical region.

Ypt/Rab GTPases and Sec1/Munc18 (SM) proteins are key components of the membrane fusion machinery. Here, we describe new mutants of the yeast SM protein Sly1 that specifically bypass the need for GTPases Ypt1 and Ypt6 in vesicular transport. All sequence alterations are confined to a short alpha-helix (alpha-20), which is conserved in fungal Sly1 proteins and, when deleted, results in GTPase suppression.

Structure-based functional analysis reveals a role for the SM protein Sly1p in retrograde transport to the endoplasmic reticulum.

Sec1p/Munc18 (SM) proteins are essential for membrane fusion events in eukaryotic cells. Here we describe a systematic, structure-based mutational analysis of the yeast SM protein Sly1p, which was previously shown to function in anterograde endoplasmic reticulum (ER)-to-Golgi and intra-Golgi protein transport. Five new temperature-sensitive (ts) mutants, each carrying a single amino acid substitution in Sly1p, were identified.

Multiple SNARE interactions of an SM protein: Sed5p/Sly1p binding is dispensable for transport.

Sec1/Munc18 (SM) proteins are central to intracellular transport and neurotransmitter release but their exact role is still elusive. Several SM proteins, like the neuronal N-Sec1 and the yeast Sly1 protein, bind their cognate t-SNAREs with high affinity. This has been thought to be critical for their function.

The GAP activity of Msb3p and Msb4p for the Rab GTPase Sec4p is required for efficient exocytosis and actin organization.

Polarized growth in Saccharomyces cerevisiae is thought to occur by the transport of post-Golgi vesicles along actin cables to the daughter cell, and the subsequent fusion of the vesicles with the plasma membrane. Previously, we have shown that Msb3p and Msb4p genetically interact with Cdc42p and display a GTPase-activating protein (GAP) activity toward a number of Rab GTPases in vitro. We show here that Msb3p and Msb4p regulate exocytosis by functioning as GAPs for Sec4p in vivo.

The riddle of the Sec1/Munc-18 proteins - new twists added to their interactions with SNAREs.

Sec1/Munc-18 (SM) proteins are essential for intracellular membrane fusion reactions. Most of them bind to membrane-associated soluble N-ethylmaleimide-sensitive fusion (NSF)-attachment protein receptors (SNAREs) of the syntaxin subfamily but it is unclear whether regulating syntaxins is their primary role. Recent studies now have shown that the mechanism of syntaxin binding is not conserved, even though the structures of both protein families are.