Explore protein folding through energy landscape funnels, HP model simulation, and free energy minimization
Proteins fold from disordered chains into unique 3D structures. The native structure corresponds to the global minimum of free energy G. Anfinsen's dogma (1972) states the amino acid sequence alone determines the folded structure — the thermodynamic hypothesis.
The energy landscape is a funnel-shaped surface mapping each conformation to its free energy. The funnel guides folding: many high-energy unfolded states converge toward fewer low-energy states near the native fold. Ruggedness (local minima) causes kinetic traps. Frustration (competing interactions) determines landscape roughness.
The core HP lattice model (Dill 1985) classifies residues as Hydrophobic (H) or Polar (P) and uses non-bonded H-H contacts as its main stabilizing term. This page keeps that HP core, then optionally adds a simple nonlocal P-P contact bonus as a toy proxy for extra stabilization. It is still a qualitative teaching model, not a chemically faithful force field.
Understanding energy landscapes enables rational drug design. Small molecules must bind to the native state's energy minimum. Misfolded proteins (e.g., amyloid-β in Alzheimer's) represent alternative energy minima. Designing drugs to stabilize the native basin or block aggregation pathways is a key therapeutic strategy.
AlphaFold (2020) revolutionized protein structure prediction by learning the energy landscape from evolutionary data. Before AlphaFold, the CASP competition showed gradual progress using physics-based energy functions. The folding funnel concept underpins both template-based and ab initio prediction methods.
Watch the 2D lattice: H residues (orange) try to cluster together while P residues (blue) stay exposed. The energy landscape places energy against compactness inside a stylized funnel. The energy vs step plot shows fluctuations with a downward trend. At low relative temperature, the chain gets trapped in local minima; at high relative temperature, it explores more freely.
1) Start with 'Ideal' preset and watch rapid folding to low energy. 2) Switch to 'Frustrated' to see kinetic trapping. 3) Increase relative temperature to observe unfolding — the chain escapes local minima. 4) Increase the polar-contact bonus to see how the toy model reshapes the funnel. 5) Try alternating vs block sequences: block H residues usually compact more easily.