Gyp8 is a Membrane-anchored Rab GAP (GTPase Accelerating protein) whose Correct Targeting to Peroxisomes Depends Upon Chaperone Msp1

SMSU Event Center BC

Eukaryotic cells use vesicular transport pathways to build and maintain membrane-bound organelles that house specific biochemical functions. Rab GTPase signaling proteins (Rabs) are key regulators of vesicular transport, controlling where and whether membranes can dock and fuse, delivering lipid and protein contents to the appropriate destination. Rabs adopt their active conformation when bound to GTP, which allows Rab interactions with tethering and membrane fusion proteins. Rab proteins have a slow intrinsic rate of hydrolyzing GTP to GDP, so Rabs depend upon GTPase accelerating proteins (GAPs) to trigger GTP hydrolysis and return the Rab to an inactive state. Rab GAPs are important to regulate the efficiency and fidelity of transport pathways, and defective Rab GAPs are implicated in a variety of human diseases. We report that the yeast Rab GAP Gyp8 is a transmembrane protein whose association with peroxisomes is regulated by the ATPase Msp1, a chaperone that functions to remove tail-anchored proteins from peroxisomes and mitochondria. Fluorescence microscopy indicated that GFP-tagged Gyp8 co-localized with peroxisomal markers in wild type cells. Computational analysis of Gyp8 hydrophobicity predicts a single-pass transmembrane domain near the carboxy terminus, characteristic of a tail- anchored protein and similar to the human ortholog. Subcellular fractionation biochemically demonstrated that Gyp8 localized exclusively to a membrane fraction that contains peroxisomes and is resistant to membrane extraction. These data represent the first report in any experimental system of a Rab GAP that localizes to peroxisomes. Further study will explore the presumptive physiological role of Gyp8 in regulating peroxisome dynamics.