Proteomic analysis of human sperm reveals changes in protamine 1 phosphorylation in men with infertility

OBJECTIVE:To perform a comprehensive assessment of protamine (P) isoforms and modifications in human sperm with the aim of identifying how P modifications and isoforms are altered in men with reduced sperm motility and low sperm count. DESIGN:Cross-sectional. SETTING:Academic medical center. PATIENTS:A total of 18 men with prior reported pregnancy and normozoospermia (normal sperm), 14 men from couples with infertility and asthenozoospermia (reduced sperm motility), and 24 men from couples with infertility and oligoasthenoteratozoospermia (low sperm count and motility and abnormal sperm morphology). INTERVENTION(S):Not applicable. MAIN OUTCOME MEASURE(S):Proteomic assessment using both top-down and bottom-up liquid chromatography mass spectrometry (MS) analysis. RESULTS:A total of 13 posttranslational modifications were identified on P1 and P2 using bottom-up MS, including both phosphorylation and methylation. Top-down MS revealed an unmodified and phosphorylated isoform of P1 and the 3 major isoforms of P2, HP2, HP3, and HP4. Protamine 1 phosphorylation was overall higher in men with male factor infertility compared with those with normal semen analysis (40.5% vs. 32.6). There was no difference in P posttranslational modifications or isoforms of P2 in men with normal vs. abnormal fertility. CONCLUSION:Human protamines bear a number of posttranslational modifications, with alterations in P1 phosphorylation noted in the setting of male factor infertility.