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. 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. May play a role in vesicular trafficking during spermatogenesis. May be involved in direct or indirect transcriptional regulation of E-cadherin (By similarity). Interacts with VPS33B. Associates with the homotypic fusion and vacuole protein sorting (HOPS) complex; impaired by VPS33B. Interacts with RAB11A (By similarity). Colocalizes in clusters with VPS33B at cytoplasmic organelles. Belongs to the SPE39 family.