Two Subunits Contribute to the Integrity of the TRAPP II complex

Intracellular protein transport in yeast is a highly regulated process controlled by several layers of regulatory elements, most of which are conserved in higher eukaryotes. The master regulators of transport are Rab GTPases, which are in turn regulated by other factors known as GEFs and GAPs. In this dissertation, I report the findings of research pertaining to a large protein complex acting as a GEF on multiple Rab GTPases in yeast. This complex, known as TRAPP, is found in three alternative arrangements, each governing a different transport step. One such arrangement, TRAPP II, contains 11 conserved subunits, 8 of which are essential for viability. However, the precise architecture of this complex remains poorly understood, as do the specific roles of two subunits, Trs20 and Trs33, in the context of the TRAPP complex. Here I provide and discuss evidence clarifying the functions of Trs33 and Trs20. Using approaches involving yeast genetics, protein biochemistry, and fluorescence microscopy, I demonstrate that each subunit contributes to the structure and function of TRAPP II through novel interactions with a third subunit, Trs120. Moreover, a mutation in TRS20, analogous to one which causes a disease in humans, disrupts the interaction of Trs20 with Trs120. Together, these results shed light on the structural interdependencies of the TRAPP II complex, and elucidate the roles of two subunits in the structure and function of this complex. In addition, the finding of defective interaction between Trs20 and Trs120 caused by a disease-associated mutation has implications for further research into the molecular basis of the disease, as well as possible therapeutic targets.