A novel motif at the C-terminus of palmitoyltransferases is essential for Swf1 and Pfa3 function in vivo

JAVIER VALDEZ TAUBAS

Andover, NH

Congreso; Gordon Research Conference. Molec. Membrane Biology; 2009

GRC

S-acylation (commonly known as palmitoylation) is a widespread posttranslational modification that consists of the addition of a lipid molecule to cysteine residues of a protein through a thioester bond. This modification is predominantly mediated by a family of proteins referred to as Palmitoyltransferases (PATs). Most PATs are polytopic membrane proteins, with 4-6 transmembrane domains, a conserved DHHC motif and variable C-and N-terminal regions, that are likely responsible for conferring localisation and substrate specificity. There is very little additional information on the structure-function relations of PATs. Swf1 and Pfa3 are yeast members of the DHHC family of proteins. Swf1 is responsible for the S-acylation of several transmembrane SNARES and other integral membrane proteins. Pfa3 is required for the palmitoylation of Vac8, a protein involved in vacuolar fusion. Here we describe a novel 16 amino acid motif present at the cytosolic C-terminus of PATs, that is required for Swf1 and Pfa3 function in vivo. Within this motif, we have identified a single residue in Swf1, Y323, as essential for function, and this is correlated with lack of palmitoylation of Tlg1, a SNARE that is a substrate of Swf1. The equivalent mutation in Pfa3 also affects its function. These mutations are the first phenotype affecting mutations uncovered that do not lie within the DHHC domain, for these or any other PATs. The motif is conserved in 70% of PATs from all eukaryotic organisms analysed, and may have once been present in all PATs. We named this motif ?Palmitoyltransferase Conserved C-Terminus? (PaCCT).