Plays an important role in sperm motility and male fertility (PubMed:34446558). Required for sperm midpiece flexibility and for the localization of sperm calcineurin to the mitochondria (PubMed:34446558). Promotes mitophagy as well as acts as an autophagy mediator in male germline cells (PubMed:33087875). Links damaged mitochondria to autophagosomes via its binding to the outer mitochondrial membrane protein VDAC2, as well as to key autophagy machinery component ATG16L1 (PubMed:33087875). Interacts (via PQIIIT motif) with PPP3R2 and PPP3CC (PubMed:34446558). Interacts with VDAC2 (PubMed:34446558, PubMed:33087875). Interacts with ATG16L1 (via WD repeats) (PubMed:33087875). Interacts with PPP3R1, PPP3CA and PPP3CB (By similarity). Predominantly expressed in the testis (at protein level) (PubMed:23844118, PubMed:34446558, PubMed:33087875). Expressed in the sperm midpiece (at protein level) (PubMed:34446558, PubMed:33087875). Mainly expressed in the postpartum and adult testis. Predominantly expressed in the spermatocytes, as well as spermatogonia and round spermatids (at protein level). Expression increases during the first wave of the spermatogenesis. Mice exhibit reduced sperm motility because of an inflexible midpiece, leading to impaired male fertility (PubMed:34446558). Spata33 knockout in Sertoli cells and spermatogenic cells suppresses mitophagy (PubMed:33087875).