Histone is a scaffold protein that constitutes nucleosomes with DNA in
the cell nucleus. When forming histone, hetero octamer is assisted by
histone chaperone proteins. As a histone chaperone protein, the crystal
structure of yeast nucleosome assembly protein (yNap1) has been
determined. For yNap1, a nuclear export signal/sequence (NES) has been
identified as a part of the long -helix. Experimental evidence via
mutagenesis on budding yeast suggests the NES is necessary for transport
out from the cell nucleus. However, the NES is masked by a region
defined as an accessory domain (AD). In addition, the role of the AD in
nuclear transport has not been elucidated yet. To address the role of
the AD, we focused on phosphorylation in the AD because proteome
experiments have identified multiple phosphorylation sites of yNap1. To
computationally treat phosphorylation, we performed all-atom molecular
dynamics (MD) simulations for a set of non-phosphorylated and
phosphorylated yNap1 (Nap1-nonP and Nap1-P). As an analysis, we
addressed how the NES is exposed to the protein surface by measuring its
solvent-access surface area (SASA). As a result, there was a difference
in the SASA distributions between both systems. Quantitatively, the
median of the SASA distribution of Nap1-P was greater than that of
Nap1-nonP, meaning that phosphorylation in the AD exposed to the NES,
resulting in increasing its accessibility. In conclusion, yNap1 might
modulate the accessibility of the NES by dislocating the AD through
phosphorylation.
Phosphorylation in the accessory domain of yeast histone chaperone protein 1 exposes the nuclear export signal sequence
