Phosphorylation in the accessory domain of yeast histone chaperone protein 1 exposes the nuclear export signal sequence
Sho Ashida1†, Rikuri Morita2†, Yasuteru Shigeta2, and Ryuhei Harada2*
1College of Biological Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-0821, Japan
2Center for Computational Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8577, Japan
These authors contributed equally to this work.
*Correspondence: Ryuhei Harada, Center for Computational Sciences, University of Tsukuba,
1-1-1 Tennodai, Tsukuba, Ibaraki 305-8577, Japan.
E-mail:ryuhei@ccs.tsukuba.ac.jp
A short running title: Phosphorylation effect on yNap1
Keywords: Histone chaperone, Phosphorylation, Molecular dynamics, Nuclear export signal/sequence
Total number of manuscript pages: 17 (including References section)
Number of figures: 4
Number of supplementary figures: 1
Abstract
Histone chaperone proteins assist in the formation of the histone octamers, the scaffold proteins that facilitate the packing of DNA into nucleosomes in the cell nucleus. One such histone chaperone protein is yeast nucleosome assembly protein 1 (yNap1), the crystal structure of which has been determined and found to have a nuclear export signal (NES) sequence within its long α-helix. Experimental evidence obtained from mutagenesis studies of the budding yeast suggests that the NES is necessary for the transport of yNap1 from the cell nucleus to the cytosol. However, the NES sequence is masked by an accessory domain, the exact role of which has not yet been elucidated, especially in nucleocytoplasmic transport. To clarify the role of the accessory domain, we focused on its phosphorylation because proteomic experiments have identified multiple phosphorylation sites on yNap1. To study this phenomenon computationally, all-atom molecular dynamics simulations of the non-phosphorylated yNap1 (Nap1-nonP) and phosphorylated yNap1 (Nap1-P) systems were performed. Specifically, we addressed how the NES sequence is exposed to the protein surface by measuring its solvent-accessible surface area (SASA). It was found that the median of the SASA distribution of Nap1-P was greater than that of Nap1-nonP, indicating that phosphorylation in the accessory domain exposes the NES, resulting in its increased accessibility. In conclusion, yNap1 might modulate the accessibility of the NES by dislocating the accessory domain through its phosphorylation.