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Binding affinity prediction by means of computer simulation has been increasingly incorporated in drug discovery projects. Its wide application, however, is limited by the prediction accuracy of the free energy calculations. The main error sources are force fields used to describe molecular interactions and incomplete sampling of the configurational space. Organic host-guest systems have been used to address force field quality because they share similar interactions found in ligands and receptors, and their rigidity facilitates configurational sampling. Here, we test the binding free energy prediction accuracy for 14 guests with aromatic or adamantane core and the CB7 host using molecular electron density derived non-bonded force field parameters. We developed a computational workflow written in Python to derive atomic charges and Lennard-Jones parameters with the minimal basis iterative stockholder method using the polarized electron density of several configurations of each guest in the bound and unbound state. The resulting non-bonded force field parameters improve binding affinity prediction, especially for guests with adamantane core in which repulsive exchange and dispersion interactions to the host dominate.

Significance Mechanism of the loss of activity of the most severe patient-derived mutants of glucose-6-phosphate dehydrogenase (G6PD) deficiency has remained elusive despite the availability of the G6PD structures for decades. Structural and biophysical investigations have revealed a common mechanism and dynamics of how these mutations hinder the substrate-binding site, reducing enzymatic activity. These are triggered by a long-distance propagation of structural defects at the dimer interface and the binding site of the noncatalytic cofactor. These structural distortions are found among all of the class I mutants investigated, providing critical clues for drug design to address G6PD deficiency by correcting the structural defects., Glucose-6-phosphate dehydrogenase (G6PD) deficiency is the most common blood disorder, presenting multiple symptoms, including hemolytic anemia. It affects 400 million people worldwide, with more than 160 single mutations reported in G6PD. The most severe mutations (about 70) are classified as class I, leading to more than 90% loss of activity of the wild-type G6PD. The crystal structure of G6PD reveals these mutations are located away from the active site, concentrating around the noncatalytic NADP+-binding site and the dimer interface. However, the molecular mechanisms of class I mutant dysfunction have remained elusive, hindering the development of efficient therapies. To resolve this, we performed integral structural characterization of five G6PD mutants, including four class I mutants, associated with the noncatalytic NADP+ and dimerization, using crystallography, small-angle X-ray scattering (SAXS), cryogenic electron microscopy (cryo-EM), and biophysical analyses. Comparisons with the structure and properties of the wild-type enzyme, together with molecular dynamics simulations, bring forward a universal mechanism for this severe G6PD deficiency due to the class I mutations. We highlight the role of the noncatalytic NADP+-binding site that is crucial for stabilization and ordering two β-strands in the dimer interface, which together communicate these distant structural aberrations to the active site through a network of additional interactions. This understanding elucidates potential paths for drug development targeting G6PD deficiency.