Paul Czodrowski

PDB2PQR: Expanding and upgrading automated preparation of biomolecular structures for molecular simulations

Real-world observable physical and chemical characteristics are increasingly being calculated from the 3D structures of biomolecules. Methods for calculating pKa values, binding constants of ligands, and changes in protein stability are readily available, but often the limiting step in computational biology is the conversion of PDB structures into formats ready for use with biomolecular simulation software. The continued sophistication and integration of biomolecular simulation methods for systems- and genome-wide studies requires a fast, robust, physically realistic and standardized protocol for preparing macromolecular structures for biophysical algorithms. As described previously, the PDB2PQR web server addresses this need for electrostatic field calculations (Dolinsky et al., Nucleic Acids Research, 32, W665–W667, 2004). Here we report the significantly expanded PDB2PQR that includes the following features: robust standalone command line support, improved pKa estimation via the PROPKA framework, ligand parameterization via PEOE_PB charge methodology, expanded set of force fields and easily incorporated user-defined parameters via XML input files, and improvement of atom addition and optimization code. These features are available through a new web interface (http://pdb2pqr.sourceforge.net/), which offers users a wide range of options for PDB file conversion, modification and parameterization.

Development, validation, and application of adapted PEOE charges to estimate pKa values of functional groups in protein-ligand complexes.

For routine pKa calculations of protein–ligand complexes in drug design, the PEOE method to compute partial charges was modified. The new method is applicable to a large scope of proteins and ligands. The adapted charges were parameterized using experimental free energies of solvation of amino acids and small organic ligands. For a data set of 80 small organic molecules, a correlation coefficient of r2 = 0.78 between calculated and experimental solvation free energies was obtained. Continuum electrostatics pKa calculations based on the Poisson–Boltzmann equation were carried out on a validation set of nine proteins for which 132 experimental pKa values are known. In total, an overall RMSD of 0.88 log units between calculated and experimentally determined data is achieved. In particular, the predictions of significantly shifted pKa values are satisfactory, and reasonable estimates of protonation states in the active sites of lysozyme and xylanase could be obtained. Application of the charge‐assignment and pKa‐calculation procedure to protein–ligand complexes provides clear structural interpretations of experimentally observed changes of protonation states of functional groups upon complex formation. This information is essential for the interpretation of thermodynamic data of protein–ligand complex formation and provides the basis for the reliable factorization of the free energy of binding in enthalpic and entropic contributions. The modified charge‐assignment procedure forms the basis for future automated pKa calculations of protein–ligand complexes. Proteins 2006;

Computational approaches to predict drug metabolism.

Background: Metabolism is one of the key parameters to be investigated and optimized in drug discovery projects. Metabolically unstable compounds or potential inhibitors of important enzymes should be detected as early as possible. As more compounds are synthesized than can be investigated experimentally, powerful computational methods are needed. Objective: We give an overview of state-of-the-art in-silico methods to predict experimental metabolic endpoints with a focus on the applicability in pharmaceutical industry. A macroscopic as well as a microscopic view of the metabolic fate and the interaction with metabolizing enzymes are given. Methods: Ligand-, protein- and rule-based approaches are presented. Conclusion: Although considerable progress has been made, the results of the calculations still need careful inspection. The domain of applicability of the models as well as methodological limitations have to be taken into account.

A selective chemical probe for exploring the role of CDK8 and CDK19 in human disease

There is unmet need for chemical tools to explore the role of the Mediator complex in human pathologies ranging from cancer to cardiovascular disease. Here we determine that CCT251545, a small molecule WNT-pathway inhibitor discovered through cell-based screening, is a potent and selective chemical probe for the human Mediator complex-associated protein kinases CDK8 and CDK19 with >100-fold selectivity over 291 other kinases. X-ray crystallography demonstrates a Type 1 binding mode involving insertion of the CDK8 C-terminus into the ligand binding site. In contrast to Type II inhibitors of CDK8/19, CCT251545 displays potent cell-based activity. We show that CCT251545 and close analogues alter WNT-pathway regulated gene expression and other on-target effects of modulating CDK8/19 including genes regulated by STAT1. Consistent with this we find that phosphorylation of STAT1SER727 is a biomarker of CDK8 kinase activity in vitro and in vivo. Finally, we demonstrate in vivo activity of CCT251545 in WNT-dependent tumors.

TRAPP: A Tool for Analysis of Transient Binding Pockets in Proteins

We present TRAPP (TRAnsient Pockets in Proteins), a new automated software platform for tracking, analysis, and visualization of binding pocket variations along a protein motion trajectory or within an ensemble of protein structures that may encompass conformational changes ranging from local side chain fluctuations to global backbone motions. TRAPP performs accurate grid-based calculations of the shape and physicochemical characteristics of a binding pocket for each structure and detects the conserved and transient regions of the pocket in an ensemble of protein conformations. It also provides tools for tracing the opening of a particular subpocket and residues that contribute to the binding site. TRAPP thus enables an assessment of the druggability of a disease-related target protein taking its flexibility into account.

Discovery of Potent, Selective, and Orally Bioavailable Small-Molecule Modulators of the Mediator Complex-Associated Kinases CDK8 and CDK19

The Mediator complex-associated cyclin-dependent kinase CDK8 has been implicated in human disease, particularly in colorectal cancer where it has been reported as a putative oncogene. Here we report the discovery of 109 (CCT251921), a potent, selective, and orally bioavailable inhibitor of CDK8 with equipotent affinity for CDK19. We describe a structure-based design approach leading to the discovery of a 3,4,5-trisubstituted-2-aminopyridine series and present the application of physicochemical property analyses to successfully reduce in vivo metabolic clearance, minimize transporter-mediated biliary elimination while maintaining acceptable aqueous solubility. Compound 109 affords the optimal compromise of in vitro biochemical, pharmacokinetic, and physicochemical properties and is suitable for progression to animal models of cancer.

hERG Me Out

A detailed analysis of the hERG content inside the ChEMBL database is performed. The correlation between the outcome from binding assays and functional assays is probed. On the basis of descriptor distributions, design paradigms with respect to structural and physicochemical properties of hERG active and hERG inactive compounds are challenged. Finally, classification models with different data sets are trained. All source code is provided, which is based on the Python open source packages RDKit and scikit-learn to enable the community to rerun the experiments. The code is stored on github ( https://github.com/pzc/herg_chembl_jcim).

Structure of the epimerization domain of tyrocidine synthetase A.

Tyrocidine, a macrocyclic decapeptide from Bacillus brevis, is nonribosomally assembled by a set of multimodular peptide synthetases, which condense two D-amino acids and eight L-amino acids to produce this membrane-disturbing antibiotic. D-Phenylalanine, the first amino acid incorporated into tyrocidine, is catalytically derived from enzyme-bound L-Phe by the C-terminal epimerization (E) domain of tyrocidine synthetase A (TycA). The 1.5 Å resolution structure of the cofactor-independent TycA E domain reveals an intimate relationship to the condensation (C) domains of peptide synthetases. In contrast to the latter, the TycA E domain uses an enlarged bridge region to plug the active-site canyon from the acceptor side, whereas at the donor side a latch-like floor loop is suitably extended to accommodate the αIII helix of the preceding peptide-carrier domain. Additionally, E domains exclusively harbour a conserved glutamate residue, Glu882, that is opposite the active-site residue His743. This active-site topology implies Glu882 as a candidate acid-base catalyst, whereas His743 stabilizes in the protonated state a transient enolate intermediate of the L↔D isomerization.

Chasing Protons: How Isothermal Titration Calorimetry, Mutagenesis, and pKa Calculations Trace the Locus of Charge in Ligand Binding to a tRNA-Binding Enzyme.

Drug molecules should remain uncharged while traveling through the body and crossing membranes and should only adopt charged state upon protein binding, particularly if charge-assisted interactions can be established in deeply buried binding pockets. Such strategy requires careful pKa design and methods to elucidate whether and where protonation-state changes occur. We investigated the protonation inventory in a series of lin-benzoguanines binding to tRNA-guanine transglycosylase, showing pronounced buffer dependency during ITC measurements. Chemical modifications of the parent scaffold along with ITC measurements, pKa calculations, and site-directed mutagenesis allow elucidating the protonation site. The parent scaffold exhibits two guanidine-type portions, both likely candidates for proton uptake. Even mutually compensating effects resulting from proton release of the protein and simultaneous uptake by the ligand can be excluded. Two adjacent aspartates induce a strong pKa shift at the ligand site, resulting in protonation-state transition. Furthermore, an array of two parallel H-bonds avoiding secondary repulsive effects contributes to the high-affinity binding of the lin-benzoguanines.

Discovery of potent and selective CDK8 inhibitors from an HSP90 pharmacophore

Here we describe the discovery and optimization of 3-benzylindazoles as potent and selective inhibitors of CDK8, also modulating CDK19, discovered from a high-throughput screening (HTS) campaign sampling the Merck compound collection. The primary hits with strong HSP90 affinity were subsequently optimized to potent and selective CDK8 inhibitors which demonstrate inhibition of WNT pathway activity in cell-based assays. X-ray crystallographic data demonstrated that 3-benzylindazoles occupy the ATP binding site of CDK8 and adopt a Type I binding mode. Medicinal chemistry optimization successfully led to improved potency, physicochemical properties and oral pharmacokinetics. Modulation of phospho-STAT1, a pharmacodynamic biomarker of CDK8, was demonstrated in an APC-mutant SW620 human colorectal carcinoma xenograft model following oral administration.