LYZL4 (lysozyme-like 4) is a c-type lysozyme family member predominantly expressed in the male reproductive tract, particularly testis and epididymis 1. Unlike canonical lysozymes, LYZL4 lacks detectable bacteriolytic and muramidase activities in vitro 23, despite retaining the characteristic c-type lysozyme structure with four disulfide bridges 4. LYZL4 is localized to the acrosomal region of spermatids and the acrosomal membrane of mature spermatozoa 25, where it functions as a multi-functional protein. Immunoneutralization studies demonstrate LYZL4's role in sperm-egg binding and fertilization, with antibody-mediated inhibition reducing human sperm binding to zona-free hamster eggs in a dose-dependent manner 56. Biochemically, recombinant LYZL4 exhibits potent hyaluronan binding ability and strong free radical scavenging capacity 54, suggesting protective functions during sperm transport and fertilization. Recently, LYZL4 has emerged as a therapeutic target beyond reproduction: microglial LYZL4 is upregulated in Alzheimer's disease and facilitates amyloid-β clearance, with LYZL4 overexpression reducing Aβ burden both in vitro and in vivo 7. Thus, LYZL4 represents a functionally divergent lysozyme-like protein with dual roles in male reproduction and neuroinflammatory disease.