Mapping of Post-translational Modifications of Transition Proteins, TP1 and TP2 and Identification of Protein Arginine Methyltransferase 4 and Lysine Methyltransferase 7 as Methyltransferase for TP2 [DNA and Chromosomes]

March 28th, 2015 by Nikhil, G., Pradeepa, M. M., Anayat, B. U., Satyanarayana, R. M. R.

In a unique global chromatin remodeling process during mammalian spermiogenesis, 90% of the nucleosomal histones are replaced by testis-specific transition proteins, TP1, TP2 and TP4. These proteins are further substituted by sperm-specific protamines, P1 and P2,to forma highly condensed sperm chromatin. In spermatozoa, a small proportion of chromatin, which ranges from 1-10% in mammals, retain the nucleosomal architecture and is implicated to play a role in transgenerational inheritance. However, there is still no mechanistic understanding about the interaction of chromatin machinery with histones and transition proteins,which facilitate this selective histone replacement from chromatin.Here, we report the identification of 16 and 19 novel post-translational modifications on rat endogenous transition proteins, TP1 and TP2 respectively, by mass spectrometry. By in vitro assays and mutational analysis, we demonstrate that protein arginine methyltransferase PRMT4 (CARM1) methylates TP2 at Arg71, Arg75 and Arg92 residues and lysine methyltransferase KMT7 (Set9) methylates TP2 at Lys88 and Lys91 residues. Further studies with modification specific antibodies which recognize TP2K88me1 and TP2R92me1 modifications showed that they appear in elongating to condensing spermatids and is predominantly associated with the chromatin bound TP2. This work establishes the repertoire of PTMs that occur on TP1 and TP2, which may play a significant role in various chromatin templated events during spermiogenesis and in the establishment of the sperm epigenome.
  • Posted in Journal of Biological Chemistry, Publications
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