Gyp1p

Gyp1p is a Rab GTPase-activating protein (RabGAP) in the budding yeast Saccharomyces cerevisiae. It is encoded by the GYP1 gene and belongs to the GYP family of RabGAPs that regulate Rab GTPases involved in vesicular trafficking. As a GAP, Gyp1p stimulates the GTPase activity of Rab proteins, promoting hydrolysis of GTP to GDP and thereby inactivating the Rab GTPase to control the timing and specificity of vesicle docking and fusion events.

Biochemically, Gyp1p contains a conserved RabGAP catalytic domain of the TBC family, which is essential for its activity, and additional regions that mediate interactions with membranes and other trafficking factors. It is largely cytosolic but can associate with membranes, often in a Rab-dependent manner, positioning it to regulate Rab activity on membranes of the early secretory pathway.

Genetic and cell biology studies place Gyp1p in the regulation of ER-to-Golgi and related trafficking steps, acting on Rab1 family members such as Ypt1p and potentially other Rab GTPases. Through its GAP activity, Gyp1p contributes to the coordination of vesicle budding, targeting, and fusion within the yeast endomembrane system, and interacts with other Rab regulators and effector proteins to maintain trafficking efficiency and organelle homeostasis.

The GYP gene family includes multiple GYP proteins with overlapping and distinct RabGAP specificities, reflecting a complex network that governs Rab GTPase signaling in yeast.