Improving the accuracy of pose prediction in molecular docking via structural filtering and conformational clustering

Sunsetting Binding MOAD with its last data update and the addition of 3D-ligand polypharmacology tools

Binding MOAD is a database of protein-ligand complexes and their affinities with many structured relationships across the dataset. The project has been in development for over 20 years, but now, the time has come to bring it to a close. Currently, the database contains 41,409 structures with affinity coverage for 15,223 (37%) complexes. The website BindingMOAD.org provides numerous tools for polypharmacology exploration. Current relationships include links for structures with sequence similarity, 2D ligand similarity, and binding-site similarity. In this last update, we have added 3D ligand similarity using ROCS to identify ligands which may not necessarily be similar in two dimensions but can occupy the same three-dimensional space. For the 20,387 different ligands present in the database, a total of 1,320,511 3D-shape matches between the ligands were added. Examples of the utility of 3D-shape matching in polypharmacology are presented. Finally, plans for future access to the project data are outlined.

Crystal structure of the plant feruloyl-coenzyme A monolignol transferase provides insights into the formation of monolignol ferulate conjugates

Lignin is a highly complex phenolic polymer which is essential for plants, but also makes it difficult for industrial processing. Engineering lignin by introducing relatively labile linkages into the lignin backbone can render it more amenable to chemical depolymerization. It has been reported that introducing a feruloyl-coenzyme A monolignol transferase from Angelica sinensis (AsFMT) into poplar could incorporate monolignol ferulate conjugates (ML-FAs) into lignin polymers, suggesting a promising way to manipulate plants for readily deconstructing. FMT catalyzes a reaction between monolignols and feruloyl-CoA to produce ML-FAs and free CoA-SH. However, the mechanisms of substrate specificity and catalytic process of FMT remains poorly understood. Here we report the structure of AsFMT, which adopts a typical fold of BAHD acyltransferase family. Structural comparisons with other BAHD homologs reveal several unique structural features of AsFMT, different from those of the BAHD homologs. Further molecular docking studies showed that T375 in AsFMT may function as an oxyanion hole to stabilize the reaction intermediate and also proposed a role of H278 in the binding of the nucleophilic hydroxyl group of monolignols. Together, this study provides important structural insights into the reactions catalyzed by AsFMT and will shed light on its future application in lignin engineering.

Crystal Structure of the Chloroplastic Glutamine Phosphoribosylpyrophosphate Amidotransferase GPRAT2 From Arabidopsis thaliana

Chloroplastic glutamine phosphoribosylpyrophosphate amidotransferase (GPRATase) catalyzes the first committed step of de novo purine biosynthesis in Arabidopsis thaliana, and DAS734 is a direct and specific inhibitor of AtGPRAT, with phytotoxic effects similar to the leaf beaching phenotypes of known AtGPRAT genetic mutants, especially cia1 and atd2. However, the structure of AtGPRAT and the inhibition mode of DAS734 still remain poorly understood. In this study, we solved the structure of AtGPRAT2, which revealed structural differences between AtGPRAT2 and bacterial enzymes. Kinetics assay demonstrated that DAS734 behaves as a competitive inhibitor for the substrate phosphoribosyl pyrophosphate (PRPP) of AtGPRAT2. Docking studies showed that DAS734 forms electrostatic interactions with R264 and hydrophobic interactions with several residues, which was verified by binding assays. Collectively, our study provides important insights into the inhibition mechanism of DAS734 to AtGPRAT2 and sheds light on future studies into further development of more potent herbicides targeting Arabidopsis GPRATases.

Crystal structure of the multifunctional SAM-dependent enzyme LepI provides insights into its catalytic mechanism

Pericyclic reactions are among the most powerful synthetic transformations widely applied in the synthesis of multiple regioselective and stereoselective carbon-carbon bonds. LepI is a recently identified S-adenosyl-l-methionine (SAM)-dependent enzyme, which could catalyze dehydration, Diels-Alder reaction, and the retro-Claisen rearrangement reactions. However, the mechanism underlying these reactions by LepI remains elusive. Here we report the structure of LepI in complex with SAM as its co-factor, which adopts a typical class I methyltransferase fold. Docking studies are performed to investigate the binding modes of various substrates/products and provide insights into the catalytic mechanism of the multiple reactions catalyzed by LepI. Our study suggests that the dehydration reaction may start from the deprotonation of the hydroxyl group on the pyridone ring of the substrate by LepI^H133, during which R295 and D296 play important roles in substrate binding and stabilizing the reaction intermediate. The stereoselective dehydration is accomplished through the trans-conformer of the leaving alcohol group which is trapped by nearby residues. The pericyclic reactions following dehydration are facilitated by the hydrophobic and hydrophilic interactions in the binding pocket. H133 and R295, two residues not conserved in other methyltransferases, might account for the unique activity of LepI among the SAM-dependent methyltransferase family. Together, this study provides important structural insights into the unique reactions catalyzed by LepI and will shed light on the knowledge of mechanisms of pericyclic reactions.

Crystal structure of the nitrile-specifier protein NSP1 from Arabidopsis thaliana

As important components of the glucosinolate-myrosinase system, specifier proteins mediate plant defense against herbivory and pathogen attacks. After tissue disruption, glucosinolates are hydrolyzed by myrosinases to instable aglucones, which will rearrange to form defensive isothiocyanates. Nevertheless, this reaction could be redirected to form other products by specifier proteins. Up to now, identified specifier proteins include epithiospecifier proteins (ESPs), thiocyanate forming proteins (TFPs), and nitrile-specifier proteins (NSPs). Recently, the structures of ESP and TFP have been reported. However, both the structure and the catalytic mechanism of NSPs remain enigmatic. Here, we solved the crystal structure of the NSP1 protein from Arabidopsis thaliana (AtNSP1). Structural comparisons with ESP and TFP proteins revealed several structural features of AtNSP1 different from those of the two proteins. Subsequent molecular docking studies showed that the R292 residue in AtNSP1 displayed a conformation different from those of the corresponding residues in ESP and TFP proteins, which might account for the product specificity and catalytic mechanism of AtNSP1. Taken together, the present study provides important insights into the molecular mechanisms underlying the different product spectrums between NSPs and the other two types of specifier proteins, and shed light on the future studies of the detailed mechanisms of other specifier proteins.

Binding site druggability assessment in fragment-based drug design

Target druggability refers to the propensity that a particular target is amenable to bind high-affinity drug-like molecules. A robust yet accurate computational assessment of target druggability would greatly benefit the fields of chemical genomics and drug discovery. Here, we illustrate a structure-based computational protocol to quantitatively assess the target binding-site druggability via in silico screening a fragment-like compound library. In particular, we provide guidelines, suggestions, and critical thoughts on different aspects of this computational protocol, including: construction of fragment library, preparation of target structure, in silico fragment screening, and analysis of druggability.