Identifying Potential Binding Partners of VPS16B and VPS33B in Mammalian Cells

Platelets contain specialized granules that are required for platelet function in hemostasis. These granules are formed in the megakaryocyte precursor, and VPS33B and VPS16B are essential for this process as mutations in them cause arthrogryposis, renal dysfunction and cholestasis syndrome, where platelets lack α-granules. Here, it is shown that VPS33B and VPS16B exist as part of two complexes (480 kDa and 720 kDa). My project entailed the identification of the components of these complexes that could be required for platelet granule biogenesis. It was found that these complexes are distinct from the VPS33A HOPS complex as they are not associated with VPS11 or VPS18, but are formed through self-oligomerization. Yeast three hybrid and co-immunoprecipitation experiments suggest that VPS52, COG5 and ATP6AP2 may interact with VPS33B and VPS16B. In addition, VPS33B and VPS16B likely interact with Rab5 and/or Rab7, but not with Rab11A, based on both GST-pulldown assays and co-immunoprecipitation experiments.MAS