However, brief treatments with nocodazole actually increase CPC recruitment

s r increases, the summed value approaches 42, which is the total number of traced residues for each tail. The accumulated values for charged, neutral residue groups are shown separately. To see this figure in color, go online. tethered at the inner capsid surface, and 34 is the C-terminal residue. As expected, the empty capsid shows higher overall CTD exposure compared to the NC. Assuming that the RNA content is mainly responsible for the deviation between the empty capsid and the NC, we find that the attraction between CTDs and RNA internalizes more than half of the exposed CTD segments in the empty capsid. In the latter case, the exposed ratio peaks around the 2126th residues, which overlap with a typical binding motif of SRPK. Schematically, Fig. 5 depicts the distribution of CTD residues for the empty capsid according to our DFT calcula- tions. Because the PubMed ID: end residues have a lower exposure rate than the 2126th residues, a CTD tail must somehow bend in the middle, making it have a hook-like shape. The bent structure increases the possibility of the motif to contact with the SRPK. According to our DFT predictions, ~30% present of the residues in such motif are within the reach of the SRPK kinase. The in vitro study by Chen et al. indicated the transient CTD location in HBV capsids. It revealed the association of SRPK on the outer MedChemExpress LY-411575 surface of the empty capsid, mediated by the enzyme-binding motif in the CTD. The same assay was conducted for the NC containing RNA genome but in that case, the enzyme binding was mostly inhibited. The SRPK binding demonstrated unequivocally that the surface characteristics of the capsid changed with the CTD location. Corresponding to the experimental approach, the DFT results capture the transient feature of the capsid surface, rendering additional evidence on the interaction of CTD with SRPK. The effect of phosphorylation The CTD distribution is sensitive to the phosphorylation of serine residues. In WT capsids, three of the serine residues have been recognized as phosphorylated upon the capsid formation and packaging with pgRNA. In our DFT calculations, phosphorylation can be studied simply by setting the valence of those three serine residues from 0 to 1 for the phosphorylated case. Biophysical Journal 107 14531461 1458 Kim and Wu FIGURE 5 Schematic representation of the CTD location. Twofold capsid pore and a dimer of the capsid CP. 6 CTD tails in each twofold pore. CTD tails of the empty capsid. Here, the tails are distributed both inside and outside the empty capsid through the twofold hole. Red segments indicate the SRPK-binding motif. To see this figure in color, go online. The addition of negative charges affects both the RNA distribution and the exposure of CTD chains. Fig. 6 shows that the RNA structure inside the capsid varies significantly in response to CTD phosphorylation. Compared to the unphosphorylated case, the RNA segments become more uniformly distributed and are positioned closer to the capsid surface. CTD phosphorylation makes the RNA distribution transduced to have a relatively higher peak near the capsid surface. Phosphorylation reduces the extend CTD exposure outside the capsid. Because the addition of negative charge reduces intrachain electrostatic repulsion, the CTD brush is slightly collapsed in comparison to the unphosphorylated brush.Implication of the CTD exposure Several recent investigations presented the transient exposure of CTDs to the capsid surface. It has been post