The understanding of protein-ligand binding is of critical importance for biomedical research, yet the process itself has been very difficult to study because of its intrinsically dynamic character. Here, we have been able to quantitatively reconstruct the complete binding process of the enzyme-inhibitor complex trypsin-benzamidine by performing 495 molecular dynamics simulations of free ligand binding of 100 ns each, 187 of which produced binding events with an rmsd less than 2 Å compared to the crystal structure. The binding paths obtained are able to capture the kinetic pathway of the inhibitor diffusing from solvent (S0) to the bound (S4) state passing through two metastable intermediate states S2 and S3. Rather than directly entering the binding pocket the inhibitor appears to roll on the surface of the protein in its transition between S3 and the final binding pocket, whereas the transition between S2 and the bound pose requires rediffusion to S3. An estimation of the standard free energy of binding gives ΔG°¼ −5.2 AE 0.4 kcal∕mol (cf. the experimental value −6.2 kcal∕mol), and a two-states kinetic model k on ¼ ð1.5 AE 0.2Þ × 10 8 M −1 s −1 and k off ¼ ð9.5 AE 3.3Þ× 10 4 s −1 for unbound to bound transitions. The ability to reconstruct by simple diffusion the binding pathway of an enzyme-inhibitor binding process demonstrates the predictive power of unconventional high-throughput molecular simulations. Moreover, the methodology is directly applicable to other molecular systems and thus of general interest in biomedical and pharmaceutical research.binding affinity | distributed computing | Markov state model | transition-state kinetics | association rates U nderstanding protein-ligand binding processes is undoubtedly of critical importance in structure-based drug design, and much effort is being invested in experimental and computational methods to resolve binding. The focus has generally resided on predicting the lowest energy binding pose of a ligand (1, 2), but resolving the kinetic mechanisms and structure activity relationships of the ligand has increasingly been recognized to provide additional mechanisms for elucidating therapeutically safe and differentiated responses (3, 4). The kinetics of binding depend on the characteristic transition states of a system. Hence, characterizing the binding pathway is crucial to understanding how to control and reengineer the process of binding.Commonly used methods to experimentally determine kinetic data for biomolecular interactions are available (5), but fast timescale resolution of a binding mechanism with atomic resolution remains difficult due to the intrinsic dynamic and volatile nature of the process of binding. From a computational perspective, the difficulty lies in accurately measuring binding affinities and kinetic parameters, but it has become easier to try to predict binding free energies on a limited number of targets and to qualitatively interpret binding mechanisms using molecular dynamics. Although it still requires substantial computational reso...