Synchronized conformational fluctuations and binding site desolvation during molecular recognition

Binding site desolvation is a poorly understood prerequisite to ligand binding. Although structural fluctuations may be expected to have an important role, little is known about which fluctuations are important or the mechanism by which they promote desolvation. This investigation examines whether and how specific structural fluctuations contribute to desolvation of the ligand binding site in glycopeptide antibiotics. Backbone peptide group rotations in vancomycin, known to occur by experimental observation, were examined in this work with a two-dimensional adaptive umbrella sampling molecular dynamics simulation technique. Results indicate that energetic barriers to rotation are relatively small for two of the peptide groups intimately involved in ligand recognition. When they occur, these rotations strip water molecules away from key hydrogen bond donors and simultaneously cause significant distortions in the macrocyclic rings of the antibiotic that force water into and out of the binding site. Both events are intricately synchronized on the molecular level and have consequences that are clearly necessary to prepare the binding site for receiving a ligand. These results suggest that previously reported observations concerning structural dynamics and binding kinetics in these compounds are mechanistically linked, and they illustrate a heretofore unrecognized degree of preorganization, complexity, and synchronization that may be involved in specific molecular recognition. They also suggest that strategies for increasing antibiotic affinity through covalent dimerization may be counterproductive.