Diagram showing a mature human spermatozoon with its different parts. Previously published studies were used as a reference to summarize the list of proteins localized in different regions of the spermatozoon by immunolocalization. Proteins localized in acrosome, head, midpiece, and tail are mainly involved in capacitation and acrosomal reaction, spermatozoa-oocyte interaction (zona binding), energy production and metabolism, and motility and metabolism, respectively. The localization of a single protein at multiple sites in the sperm cell indicates its potential involvement in different physiological processes of the spermatozoon. The listed proteins include protein kinase A (PKA), phospholipase C zeta (PLC zeta), sperm head- and tail-associated protein (SHTAP), calicin, cylicins I and II, actin-capping proteins (ACP), enolase 1 (ENO1), cysteine-rich secretory protein 2 (CRISP2), arginine vasopressin receptor (AVPR), voltage-dependent anion channel (VDAC), glyceraldehyde 3-phosphate dehydrogenase (GAPDH), glutathione peroxidase 4 (GPX4), equatorial segment protein (ESP), heat shock protein 70 (HSP70), novel pyruvate kinase (PK-S), sperm acrosome membrane-associated protein 1 (SPACA1), izumo sperm-egg fusion 1 (IZUMO1), aquaporin 7 (AQPs), and the actin-related protein 2/3 complex (Arp2/3 complex).