Updated publication reference for PubMed record(s): 32727081. MTD project_description Protamines are testis-specific proteins, which replace the majority of histones during spermiogenesis. This results in a hypercondensation of the sperm DNA, finally causing a conformational change from a nucleosomal chromatin structure into a mainly toroid like structure. This is assumed to protect the paternal genome and to contribute to the formation of a hydrodynamic sperm head shape. In mice and humans, two protamines, Protamine 1 (Prm1) and Protamine 2 (Prm2), are expressed. Impaired sperm protamination has been repeatedly correlated with male subfertility in mice and humans. Apart from defects in DNA condensation and impaired DNA integrity, protamine-deficient human and murine sperm show multiple secondary defects, which cannot be explained by the chromosomal function of protamines. These include impaired sperm motility, decreased viability as well as acrsosomal malformations. In this study, we utilized a Prm2-deficient mouse model to investigate the underlying molecular mechanisms of these defects. Since trancription is silenced upon incorporation of protamines, we used LC-MS in combination with label-free quantification to compare the sperm proteome of Prm2-deficient (Prm2-/-) males with the proteome of wildtype (Prm2+/+) and Prm2 heterozygous (Prm2+/-) males. We show that Prm2 deficient mice display a strongly altered proteomic profile compared to controls. Of note, a significant downregulation of proteins SOD1 and PRDX5, which have a well-known function for the detoxification of reactive oxygen species was observed. Thus, together with a series of additional experiments, we could for the first time show that Prm2-deficiency triggers a reactive oxygen species (ROS) mediated sperm destruction cascade during epididymal sperm maturation, finally causing described secondary sperm defects.