Structural insights into the VRK1‐mediated histone phosphorylation and its regulation by mH2A1, a histone H2A variant

Abstract

Vaccinia related kinase 1 (VRK1), a mitotic protein kinase, is involved in cell proliferation, cell cycle, neuronal development, and gamatogenesis. VRK1‐induced phosphorylation of histone H3 results in nuclear condensation facilitating mitosis during cell division. To understand the VRK1's role in cell cycle transition, we studied the VRK1‐mediated histone phosphorylation and catalytic modulation by regulatory molecules. Interestingly, the VRK1 catalytic activity increases in late G2 and M phases of cell cycle and subsequently decreases at the end of anaphase. We showed that mH2A1, which is a histone H2A variant, suppresses the VRK1 activity during interphase and influences the cell cycle progression. Our NMR solution structure of human VRK1 revealed that its overall fold is similar to other VRK family kinases, VRK2 and VRK3. Despite their overall structural similarity, notable differences in their local structures were observed, in particular in the catalytic loop, activation loop and the non‐catalytic fragment at the C‐terminus of VRK1. The C‐terminal region orients around the catalytic site to be essential for its structural stability and biological activity. We showed that mH2A1 binds to the C‐terminal fragment and inhibits VRK1's catalytic activity. Hence our findings might provide structural insights into the chromatin epigenetic regulation through the VRK1‐mediated histone phosphorylation.