Component of the FTS/Hook/FHIP complex (FHF complex). The FHF complex may function to promote vesicle trafficking and/or fusion via the homotypic vesicular protein sorting complex (the HOPS complex). Regulates apoptosis by enhancing phosphorylation and activation of AKT1. Increases release of TNFSF6 via the AKT1/GSK3B/NFATC1 signaling cascade. FHF complex promotes the distribution of AP-4 complex to the perinuclear area of the cell. Component of the FTS/Hook/FHIP complex (FHF complex), composed of AKTIP/FTS, FHIP1B, and one or more members of the Hook family of proteins HOOK1, HOOK2, and HOOK3. Interacts directly with HOOK1, HOOK2 and HOOK3. The FHF complex associates with the homotypic vesicular sorting complex (the HOPS complex). Also interacts with AKT1. May interact with FHIP1A. Ubiquitous. Highest expression in kidney, testis and brain and lowest in spleen and liver. Defects in Aktip are a cause of embryonic death in homozygous animals. Death occurs at about 10 days of development. Symptoms include loss of left-right asymmetry, malformation of the developing brain and of the spinal cord, syndactyly and polydactyly. Heterozygous animals are characterized by polydactyly and thymic hyperplasia. Belongs to the ubiquitin-conjugating enzyme family. FTS subfamily. Lacks the conserved Cys residue necessary for ubiquitin-conjugating enzyme E2 activity.