Hierarchical Multi-Scale Modeling of Absolute Binding Affinity in Protein Complexes

Predicting the absolute binding affinity ($\Delta G$) of a protein-protein complex from structure alone remains challenging: physics-based simulations are costly, and experimental affinity labels are noisy and heterogeneous. We propose a hierarchical architecture that represents each complex at multi-scale resolutions-atoms, residues, chains, and the whole complex. We use distance-weighted message passing so that closer atom/residue pairs contribute more strongly, and then pool information across levels to produce a single binding affinity score. The model further incorporates transferable physicochemical priors via pretrained representations. On PPB-Affinity dataset, our method improves rank correlation over a strong baseline (Spearman's rank correlation coefficient $0.659$ vs. $0.646$). Ablations show that distance-weighted message passing, multi-scale modeling, and physically grounded representations each contribute to model performance.