Abstact

Ypt/Rab proteins are membrane-associated small GTP-binding proteins which play a central role in the coordination, activation and regulation of vesicle-mediated transport in eukaryotic cells. We present the 1.5 A high-resolution crystal structure of Ypt51 in its active, GppNHp-bound conformation. Ypt51 is an important regulator involved in the endocytic membrane traffic of Saccharomyces cerevisiae. The structure reveals small but significant structural differences compared with H-Ras p21. The effector loop and the catalytic loop are well defined and stabilized by extensive hydrophobic interactions. The switch I and switch II regions form a well-defined epitope for hypothetical effector protein binding. Sequence comparisons between the different isoforms Ypt51, Ypt52 and Ypt53 provide the first insights into determinants for specific effector binding and for fine-tuning of the intrinsic GTP-hydrolysis rate.