During my research I intend to identify the complex interaction network of tethering complexes in the endolysosomal system and to reveal the factors that defines the SNARE binding-specificity of them. Tethering factors are important participants in vesicular fusion events by bringing the donor and acceptor membranes into contact and thus facilitates the process, which will be executed by SNARE proteins. The detailed SNARE-profile of the human Vps33, which is a "core" subunit, of both HOPS and CORVET tethering complexes, is not described yet. These prompted us to identify the interacting partners of Vps33 and of the complex-specific subunits as well, using proximity labeling technique. CORVET is an early endosomal tether, while HOPS mediates homotypic fusion of late endosomes and autophagosome-lysosome fusion as well. However, the SNARE-binding subunit, Vps33 is shared. Thus we aimed to test the binding abilities of the complexes to early, late and autophagosomal SNAREs, if there is difference in binding properties of different SNAREs to CORVET and HOPS. Beside these I will investigate the relationship between the two complexes using HEK293 cells: whether overexpression one of the complex-specific subunits will influence the level of other subunits and the other complex. The endosomal transport mechanisms are under tight regulation and their malfunction lead to defective cargo delivery. Mutations in proteins that control these pathways can cause severe neurological and neurodegenerative diseases. Our work can facilitate further understanding of endosomal trafficking, vesicle fusion and SNARE-specificity of tethering complexes.