Proposed to be involved in endosomal maturation implicating in part VPS33B. In epithelial cells, the VPS33B:VIPAS39 complex may play a role in the apical RAB11A-dependent recycling pathway and in the maintenance of the apical-basolateral polarity (PubMed:20190753). May play a role in lysosomal trafficking, probably via association with the core HOPS complex in a discrete population of endosomes; the functions seems to be independent of VPS33B (PubMed:19109425). May play a role in vesicular trafficking during spermatogenesis (By similarity). May be involved in direct or indirect transcriptional regulation of E-cadherin (By similarity). Interacts with VPS33B (PubMed:19109425, PubMed:23901104). Associates with the homotypic fusion and vacuole protein sorting (HOPS) complex; impaired by VPS33B (PubMed:19109425, PubMed:23918659, PubMed:22753090). A possible interaction with VPS33A is reported conflictingly (PubMed:19109425, PubMed:23901104). Interacts with RAB11A (PubMed:20190753). Colocalizes in clusters with VPS33B at cytoplasmic organelles (PubMed:19109425). The disease is caused by variants affecting the gene represented in this entry. In liver, CEACAM5 and ABCB11 are mislocalized and E-cadherin expression is decreased. Belongs to the SPE39 family. Truncated N-terminus.