Bioinformatics: Practical Application of Simulation and Data
Mining
Protein Folding II
Prof. Corey O’HernDepartment of Mechanical Engineering & Materials
ScienceDepartment of Physics
Yale University
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What did we learn about proteins?•Many degrees of freedom; exponentially growing # of energy minima/structures•Folding is process of exploring energy landscape to find global energy minimum•Need to identify pathways in energy landscape; # of pathways grows exponentially with # of structures•Coarse-graining/clumping required
energy minimum
transition
•Transitions are temperature dependent 2
J. D. Honeycutt and D. Thirumalai, “The nature of foldedstates of globular proteins,” Biopolymers 32 (1992) 695.
T. Veitshans, D. Klimov, and D. Thirumalai, “Protein folding kinetics: timescales, pathways and energy landscapes
in terms of sequence-dependent properties,” Folding & Design 2 (1996)1.
Coarse-grained (continuum, implicit solvent, C) models for proteins
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3-letter C model: B9N3(LB)4N3B9N3(LB)5L
B=hydrophobic
N=neutral
L=hydrophilic
Nsequences= 3 ~ 1022
Np ~ exp(aNm)~1019 Number of structuresper sequence
Number of sequences forNm=46
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different mapping?
and dynamics
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Molecular Dynamics: Equations of Motion
for i=1,…Natoms
Coupled 2nd order Diff. Eq.
How are they coupled?
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(iv) Bond length potential
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Pair Forces: Lennard-Jones Interactions
ij
Parallelogramrule
-dV/drij > 0; repulsive-dV/drij < 0; attractive
force on i due to j
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‘Long-range interactions’
BB
V(r)
r/
NB, NL, NN
LL, LB
r*=21/6
hard-core
attractions-dV/dr < 0
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Bond Angle Potential
0=105
i jkijk
ijk=[0,]
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Dihedral Angle Potential
Vd(ijkl)
Vd(ijkl)
ijkl
Successive N’s
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Bond Stretch Potential
i j
for i, j=i+1, i-1
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Equations of Motion
velocityverletalgorithm
Constant Energy vs. Constant Temperature (velocity rescaling, Langevin/Nosé-Hoover thermostats)
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Collapsed Structure
T0=5h; fast quench; (Rg/)2= 5.48
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Native State
T0=h; slow quench; (Rg/)2= 7.78
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start end
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native states
Total Potential Energy
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slow quench
unfolded
native state
Radius of Gyration
Tf
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Construct the backbone in 2D
Assign sequence of hydrophobic (B) and neutral (N) residues, B residues experience an effective attraction. No bond bending potential.
Evolve system under Langevin dynamics at temperature T
Collapse/folding induced by decreasing temperatureat rate r.
BN
2-letter C model: (BN3)3B
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Energy Landscape
end-to-end distance end-to-end distance
5 contacts4 contacts 3 contacts
E/CE/C
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Rate Dependence
5 contacts
4 contacts
3 contacts2 contacts
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Misfolding
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Reliable Folding at Low Rate
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Slow rate
Fast rate
Next…
•Thermostats…Yuck!•More results on coarse-grained models•Results for atomistic models•Homework
So far…
•Uh-oh, proteins do not fold reliably…•Quench rates and potentials
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