Contemporary efforts for empirically-unbiased modeling of protein-ligand interactions entail a painful tradeoff-as reliable information on both noncovalent binding factors and the dynamic behavior of a protein-ligand complex is often beyond practical limits. We demonstrate that information drawn exclusively from static molecular structures can be used for reproducing and predicting experimentallymeasured binding affinities for protein-ligand complexes. In particular, inhibition constants (K i) were calculated for seven different competitive inhibitors of Torpedo californica acetylcholinesterase using a multiple-linear-regression-based model. The latter, incorporating five independent variables-drawn from QM cluster, DLPNO-CCSD(T) calculations and LED analyses on the seven complexes, each containing active amino-acid residues found within interacting distance (3.5 Å) from the corresponding ligand-is shown to recover 99.9% of the sum of squares for measured K i values, while having no statistically-significant residual errors. Despite being fitted to a small number of data points, leave-oneout cross-validation statistics suggest that it possesses surprising predictive value (Q 2 Loo =0.78, or 0.91 upon removal of a single outlier). This thus challenges ligand-invariant definitions of active sites, such as implied in the lock-key binding theory, as well as in alternatives highlighting shape-complementarity without taking electronic effects into account. Broader implications of the current work are discussed in dedicated appendices. Protein-ligand (PL) interactions have drawn great amounts of scientific attention throughout the last century (see refs. 1-4. for a few recent textbooks and reviews). Aside from being examined for playing crucial roles in a variety of essential biochemical processes, such interactions are often focused on in many drug design studiesrevolving around finding inhibitors for proteins such as enzymes and neuroreceptors for the purpose of invoking a desirable biological response 5-8. Due to such considerations, many researchers from a broad spectrum of scientific disciplines (consisting of computational biologists and biochemists as well as theorists from chemistry and physics) have attempted to provide some general theoretical/computational modeling schemes for predicting biochemically-relevant PL binding events 9-13. Various protein-ligand binding theories, which underlie many research efforts in the field, have been proposed. The latter include the infamous "lock-key" model, originally introduced by Fischer 14. This model has subsequently been corrected by Koshland to account for mutual, structural adaptations in both protein and ligand ("induced fit")-embracing the notion of a "glove-hand" correspondence 15,16. While more recent adjustments, taking additional conformational and solvent effects into account, have also been introduced 17-20 , none have seemed to move past the intuitive notion of shape complementarity-which clearly has undeniable didactic and predictive value, and has been imp...