Molecular Dynamics Simulation Introduction to Molecular Dynamics Simulation
Exploring the Folding Landscape Protein Folding
Uses of Molecular Dynamics Simulation: structure flexibility solvent effects chemical reactions ion channels thermodynamics (free energy changes, binding) spectroscopy NMR/crystallography
Atomic-Detail Computer Simulation Model System Molecular Mechanics Potential Energy Surface Exploration by Simulation..
Model System set of atoms explicit/implicit solvent periodic boundary conditions Potential Function empirical chemically intuitive quick to calculate Tradeoff: simplicity (timescale) versus accuracy
Lysozyme in explicit water
MM Energy Function 2/8 l q f r q i j
Newton’s Law: Fi=force on ith atom mi = mass of ith atom ai=acceleration of ith atom
Potential Function Force Newton’s Law:
Verlet’s Method Taylor:
Timescales. Bond vibrations - 1 fs Collective vibrations - 1 ps Conformational transitions - ps or longer Enzyme catalysis - microsecond/millisecond Ligand Binding - micro/millisecond Protein Folding - millisecond/second Molecular dynamics: Integration timestep - 1 femtosecond Set by fastest varying force. Accessible timescale about 100 nanoseconds.
Statistical Mechanics Observable Ensemble Average Ergodic Hypothesis: MD Simulation: 1 hr
Statistical Mechanics Observable: Ensemble Average: Probability density:
MD Simulation: Ergodic Hypothesis: e.g.:
Analysis of MD Configurations Averages Fluctuations Time Correlations
Analysis of fluctuations