RAB2B effector protein required for accurate acrosome formation and normal male fertility. Interacts (via N-terminus) with RAB2B (in GTP-bound form). 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 male fertility is significantly impaired compared with that of the controls (PubMed:34714330). Spermatozoa from mutant mice showed abnormal head shapes with an abnormal acrosome morphology (PubMed:34714330). Belongs to the GARIN family.