Molecular Basis of Action of a Small-Molecule Positive Allosteric Modulator Agonist at the Type 1 Cholecystokinin Holoreceptor.

Allosteric modulation of receptors provides mechanistic safety while effectively achieving biologic endpoints otherwise difficult or impossible to obtain by other means. The theoretical case has been made for the development of a positive allosteric modulator (PAM) of the type 1 cholecystokinin receptor (CCK1R) having minimal intrinsic agonist activity to enhance meal-induced satiety for the treatment of obesity, while reducing the risk of side effects and/or toxicity. Unfortunately, such a drug does not currently exist. In this work, we have identified a PAM agonist of the CCK1R, SR146131, and determined its putative binding mode and receptor activation mechanism by combining molecular modeling, chimeric CCK1R/CCK2R constructs, and site-directed mutagenesis. We probed the structure-activity relationship of analogs of SR146131 for impact on agonism versus cooperativity of the analogs. This identified structural features that might be responsible for binding affinity and potency while retaining PAM activity. SR146131 and several of its analogs were docked into the receptor structure, which had the natural endogenous peptide agonist, cholecystokinin, already in the bound state (by docking), providing a refined structural model of the intact CCK1R holoreceptor. Both SR146131 and its analogs exhibited unique probe-dependent cooperativity with orthosteric peptide agonists and were simultaneously accommodated in this model, consistent with the derived structure-activity relationships. This provides improved understanding of the molecular basis for CCK1R-directed drug development.

Discovery of N-substituted 7-azaindoles as PIM1 kinase inhibitors - Part I.

Novel N-substituted azaindoles have been discovered as PIM1 inhibitors. X-ray structures have played a significant role in orienting the chemistry effort in the initial phase of hit confirmation. Disclosure of an unconventional binding mode for 1 and 2, as demonstrated by X-ray crystallography, is presented and was an important factor in selecting and advancing a lead series.

Evaluation of cancer dependence and druggability of PRP4 kinase using cellular, biochemical, and structural approaches.

PRP4 kinase is known for its roles in regulating pre-mRNA splicing and beyond. Therefore, a wider spectrum of PRP4 kinase substrates could be expected. The role of PRP4 kinase in cancer is also yet to be fully elucidated. Attaining specific and potent PRP4 inhibitors would greatly facilitate the study of PRP4 biological function and its validation as a credible cancer target. In this report, we verified the requirement of enzymatic activity of PRP4 in regulating cancer cell growth and identified an array of potential novel substrates through orthogonal proteomics approaches. The ensuing effort in structural biology unveiled for the first time unique features of PRP4 kinase domain and its potential mode of interaction with a low molecular weight inhibitor. These results provide new and important information for further exploration of PRP4 kinase function in cancer.

Structure of the reduced disulfide-bond isomerase DsbC from Escherichia coli.

Disufide-bond isomerase (DsbC) plays a crucial role in folding periplasmically excreted bacterial proteins. The crystal structure of the reduced form of DsbC is presented. The pair of thiol groups from Cys98 and Cys101 that form the reversible disulfide bond in the enzymatic active site are 3.1 A apart and the electron density clearly shows that the S atoms do not form a covalent bond. The other pair of Cys residues (141 and 163) in DsbC form a disulfide bond. This is different from the previously reported crystal form of DsbC (McCarthy et al., 2000), in which both Cys pairs are oxidized. Specific hydrogen-bond interactions are identified that stabilize the active site in the reactive reduced state with the special participation of hydrogen bonds between the active-site cysteine residues (98 and 101) and threonine residues 94 and 182. The present structure also differs in the orientation of the catalytic domains within the protein dimer. This is evidence of flexibility within the protein that probably plays a role in accommodating the substrates in the cleft between the catalytic domains.