DEFB121 is a beta-defensin antimicrobial peptide characterized by six conserved cysteine residues. Based on limited published evidence, it exhibits antibacterial activity and membrane destabilizing properties 1. The protein participates in innate immune responses and cell-killing mechanisms through protein binding interactions. DEFB121 is part of a clustered gene family on chromosome 20.1, with expression restricted to the male reproductive tract where it is differentially regulated by androgens 1. The gene likely evolved through duplication events and positive selection, potentially related to reproductive specialization.