Thermodynamic and structural basis of phosphorylation-induced disorder-to-order transition in the regulatory light chain of smooth muscle myosin.
We have performed molecular dynamics simulations of the phosphorylation domain (PD) of the regulatory light chain (RLC) of smooth muscle myosin, to gain insight into the thermodynamic principles governing the phosphorylation-induced disorder-to-order transition. Simulations were performed in explicit water under near-physiological conditions, starting with an ideal alpha-helix. In the absence of phosphorylation, the helical periodicity of the peptide was disrupted at residues T9-K11, while phosphorylation significantly favored the helical periodicity, in agreement with experimental data. Using the MM/PBSA approach, we calculated a relative free energy of -7.1 kcal/mol for the disorder-to-order transition. A large enthalpic decrease was compensated by a large loss of conformational entropy, despite the small helical increase (no more than three residues) upon phosphorylation. Phosphorylation decreased the conformational dynamics of K and R side chains, especially R16, which forms a salt bridge with pS19. Mutation of R16 to A or E prevented this phosphorylation-dependent ordering. We propose that phosphorylation balances the enthalpy-entropy compensation of the disorder-to-order transition of RLC via short and long-range electrostatic interactions with positively charged residues of the phosphorylation domain. We suggest that this balance is necessary to induce a disorder-to-order conformational change through a subtle energy switching.
Espinoza-Fonseca
L Michel
LM
Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455, USA.
Kast
David
D
Thomas
David D
DD
D000595:Amino Acid Sequence; D003198:Computer Simulation; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009130:Muscle, Smooth / Q000737:chemistry / Q000378:metabolism; D018994:Myosin Light Chains / Q000737:chemistry* / Q000378:metabolism*; D010766:Phosphorylation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D013816:Thermodynamics
D018994:Myosin Light Chains