RAB2B effector protein required for accurate acrosome formation and normal male fertility (PubMed:34714330). In complex with RAB2A/RAB2B, seems to suppress excessive vesicle trafficking during acrosome formation (PubMed:34714330). Expressed in testis (at protein level). Expressed from day 21, around when spermiogenesis occurs (PubMed:34714330). Expression dramatically increases at the mid-round spermatid stage (steps 4-6) (PubMed:34714330). Mutant males are sterile (PubMed:34714330). Spermatozoa from mutant mice showed abnormal head shapes with an abnormal swollen acrosome morphology and impaired acrosome reaction (PubMed:34714330). Belongs to the GARIN family.