Global proteomic analyses of lysine acetylation, malonylation, succinylation, and crotonylation in human sperm reveal their involvement in male fertility

Protein lysine modifications (PLMs) are hotspots of post-translational modifications and are involved in many diseases; however, their role in human sperm remains obscure. This study examined the presence and functional roles of a classical PLM (lysine acetylation, Kac) and three novel PLMs (lysine malonylation, Kmal; lysine succinylation, Ksucc; lysine crotonylation, Kcr) in human sperm. Immunoblotting and immunofluorescence assays revealed modified proteins (15–150 kDa) in the tails of human sperm. An immunoaffinity approach coupled with liquid chromatography/tandem mass spectrometry revealed 1423 Kac sites in 680 proteins, 196 Kmal sites in 118 proteins, 788 Ksucc sites in 251 proteins, and 1836 Kcr sites in 645 proteins. These modified proteins participate in a variety of biological processes and metabolic pathways. Crosstalk analysis demonstrated that proteins involved in the sperm energy pathways of glycolysis, oxidative phosphorylation, the citrate cycle, fatty acid oxidation, and ketone body metabolism were modified by at least one of these modifications. In addition, these modifications were found in 62 male fertility-related proteins that weave a protein-protein interaction network associated with asthenoteratozoospermia, asthenozoospermia, globozoospermia, spermatogenic failure, hypogonadotropic hypogonadism, and polycystic kidney disease. Our findings shed light on the functional role of PLMs in male reproduction.

Significance

Protein lysine modifications (PLMs) are hotspots of posttranslational modifications and are involved in many diseases. This study revealed the presence of a classical PLM (lysine acetylation) and three novel PLMs (lysine malonylation, lysine succinylation, and lysine crotonylation) in human sperm tails. The modified proteins participate in a variety of biological processes and metabolic pathways. In addition, these modifications were found in 62 male infertility-associated proteins and could serve as potential diagnostic markers and therapeutic targets for male infertility.