The HOPS complex and Vps33 in Dictyostelium discoideum

In order for cells to eat, they must detect food at their cell surface and pull it in to form a vesicle known as an endosome. This endosome then becomes acidified to become a lysosome and eventually becomes neutral again, as a postlysosome, so that waste can be expelled from the cell. Collectively, this is referred to as the endocytic pathway. Several proteins are involved in this process – Rabs are known to mediate specificity of fusing vesicles, and SNARES catalyze the actual vesicle fusion. In this study we look at the protein Vps33, a subunit of the HOPS complex. The HOPS complex is known to interact with Rabs and SNARES, and we are interested as to where it acts within the cell. By tagging Vps33 with Green Fluorescent Protein (GFP), we can visualize its localization under the microscope. We observe here that Vps33 localizes primarily to the cytoplasm, with sparse localization to intracellular vesicles.