Consistent with the above observations in mice, we report here for
the first time the analysis of the intact (not digested) human protamine 1
amino acid sequence through MS (Figure 2). Following a similar strategy
to that used in mouse sperm, we were able to detect in human P1
mono‑, di‑ and tri‑phosphorylations by MS (Figure 2). In addition,
P1 seemed to carry combinations of different PTMs, which included
di‑acetylations with mono‑methylation and, in contrast to mouse P1,
di‑phosphorylations with mono‑acetylation (Figure 1). Concerning
human P2 family, the potential presence of PTMs (methylations
and acetylations) was only detected in the component P3 (data not
shown). Despite this evidence for the presence of phosphorylations
and acetylations in mouse (Brunner et al. 2014) and human (Figure 2)
protamines, we believe that the existence of a protamine code with
a similar function to the histone code (where PTMs are involved
in gene expression) is unlikely. The main reasons are the presence
of the semicrystalline chromatin status conferred by the nucleoprotamine
toroidal packaging and the fact that the sperm chromatin