Noncovalent interactions such as hydrogen bonds and π-π interactions are involved in the stabilization of three-dimensional structures and specific molecular recognition. We have recently developed the Negative Fragmentation Approach (NFA) to evaluate noncovalent interactions quantitatively, using quantum chemical calculations. Although NFA is effective for small and medium-sized systems, its direct application to large macromolecules such as proteins demands further refinement. Here, we extended the original NFA to evaluate noncovalent interactions in proteins by combining it with the ONIOM method. The NFA-ONIOM scheme was applied to a hydrogen bond between ∆5-3-ketosteroid isomerase and equilenin, an analogue of the intermediate.
TAKANO et al. (Thu,) studied this question.