| Sarcoplasmic reticulum Ca2+ pump (SERCA) is an important transmembrane protein for transferring calcium ions from the cytoplasmic compartment to the sarcoplasmic reticulum compartment, and its activity is regulated by phospholamban (PLN), a protein interacted with it. There are two structural states (the natural and its phosphorylated structures) in PLN due to its phosphorylation by protein kinases. In the nature conformation, PLN has an inhibitory effect on bio-activity of SERCA when they form a tight complex. In contrast, the inhibitions will lose and SERCA will recover the ability to transfer calcium ions, if PLN has been phosphorylated. PLN's three-dimensional structure in living cell is of most interests. In the current case, we have summarized the investigations on PLN structure, based on which long time-scale molecular dynamics (MD) simulations were employed to systematically study its structure.The first 22 residues from one chain of PLN bellflower structure determined by NMR experiments, as well as its phosphorylation at position 16/17 and mutation at position 9 were picked up as four different peptides. Then we used AMBER to solvate peptides in different solvent and with different ion concentration to get eight different simulation systems. Then we processed energy minimization, heating,equilibration and 10ns MD simulation for each system. Furthermore, we did 10ns MD simulations for PLN monomer and pentamer in water solution.Thought analyzing MD trajectories, we found: the 3-15 residues of the original structure retain their helix structures; the phosphorylation of both sites make the structure less ordered; in the effect of both phosphorylation and high ion concentration at the same time,the structure is more disordered; PLN monomer has two helix peptides in cytoplasmic and membrane-spanning domain; the cytoplasmic helix peptide will bent to the other one; the Leu/Ile zip motif in the membrane-spanning domain connect the five monomer tightly in this domain.
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