| Popis: |
The rab family of small, ras-like GTPases regulate membrane trafficking events in the secretory and endocytic pathways. They appear to be involved in all stages of vesicular transport, from vesicle budding and cargo selection to motility, docking and membrane fusion. Through a cycle of GTP binding and hydrolysis, rab-effector proteins are recruited to membrane sub-domains in a temporally and spatially specific manner. Several rab proteins localise to the Golgi apparatus, the organelle consisting of stacked, flattened, membrane-bound cisternae through which newly-synthesised proteins are transited and modified, and where proteins and lipids are sorted and packaged for transport to other subcellular destinations. The structure of the Golgi is maintained by a matrix of proteins, many of which have now been shown to be rab-effector proteins. This thesis focuses on Golgi-localised rab proteins and their effector proteins. The cis-Golgi-localised rab protein, rabl, is shown to interact with the Golgi matrix/golgins GM130 and p115 while rab2 binds GM130 as well as a novel tethering factor named golgin-45. siRNA-mediated depletion of these rabs and golgins revealed them to be important for the maintenance of Golgi structure and suggested that p115 is primarily recruited to Golgi membranes by its interaction with rab1 rather than its association with GM130. A search for additional rab1 effectors revealed potential interactions between rab1 and the phosphoinositide- binding/metabolising proteins centaurin?2 and MTMR6. A search for novel effectors of the trans-Golgi-localised rab protein, rab6, was also made, revealing specific interactions with the dynactin subunit p150glued and the dynactin/dynein accessory proteins BicD1 and BicD2. These interactions are proposed to mediate the recruitment of dynactin/dynein to membranous cargo and control minus-end directed, microtubule-dependent vesicle motility. An additional rab6 effector, GOPC, was also identified, which may be responsible for cargo recognition and sorting. Finally, the cis-Golgi rab-effector and matrix protein, GM130, is shown to have a hitherto unsuspected role in the activation of a family of Golgi-localised Ste20 kinases. The implications of all these interactions for Golgi structure and function is discussed. |
