The Golgi complex is the central sorting station for nearly a third of all proteins in eukaryotic cells, but how cells regulate the flow of material through this organelle remains unknown. With many human diseases arising from defects in the sub-cellular membrane and protein sorting machinery and its regulators, the lack of understanding about the regulation of Golgi function has been a stubborn block to progress. Enter Chris Fromme, Weill Institute for Cell and Molecular Biology/Molecular Biology and Genetics, whose goal is to uncover mechanisms governing the regulation of Golgi function, specifically the activation of two essential Rab proteins that control Golgi traffic: Ypt1 (Rab1) and Ypt31/32 (Rab 11).

While the protein (TRAPPI) that activates Ypt1 is established, the activator of Ypt31/32 has been the subject of controversy, as researchers have not been able to provide evidence to confirm the suspected activator, TRAPPII. But Fromme and his team have observed that TRAPPII is in fact a bone fide activator for both proteins but that it requires membranes to activate Ypt31/32, which is why it has not been previously observed by other groups. The dependence on membranes also implies the existence of an autoinhibitory mechanism. With this discovery as a jumping off point, Fromme will take the next step of inquiry: why does TRAPPII require membranes to activate Ypt31/32 and not Ypt1, and how does it activate two different substrates? Fromme will investigate these questions using in vitro assays, as well as yeast genetics and cell biology to characterize the functional consequences of perturbing TRAPPII activity in vivo.

Another related line of inquiry will be to uncover the mechanism and functional significance of TRAPPIII at the Golgi. Some evidence points to TRAPPIII as an activator for Ypt1 at the early Golgi, but more needs to be done to understand how TRAPPIII is regulated and what role it plays in the cell. Other aims include gaining a better understanding of the dynamics of TRAPP complexes with interacting partners, specifically whether they are regulated by crosstalk with other Golgi-localized GTPases. The overall goal of the project is to provide a new, comprehensive model for the regulation of the essential Golgi Rab trafficking pathways.  NIH Award Number: 1R01GM116942-01