Jing-Fang Wang

Molecular dynamics studies on the interactions of PTP1B with inhibitors: from the first phosphate-binding site to the second one

Protein tyrosine phosphatases 1B (PTP1B) is a major negative regulator of both insulin and leptin signaling pathways. In view of this, it becomes an important target for drug development against cancers, diabetes and obesity. The aim of the current study is to use the long time-scale molecular dynamics (MD) simulations to investigate the structural and dynamic factors that cause its inhibition by INTA and INTB, the two most potent and highly selective PTP1B inhibitors known so far. In order to investigate the mode of collective motions that is vitally important to the biological function, the covariance matrix of C(alpha) atoms was introduced for performing the dynamic analysis of the inhibition systems. It has been observed that the conformational and dynamic features of WPD-Loop, R-Loop and S-Loop play a key role in providing a smooth entrance for the inhibitors moving into the binding pocket as well as a favorable microenvironment to stabilize them. Furthermore, the hydrogen bonding networks formed around the active site with INTA and INTB may be the main reason of why the inhibition of PTP1B by the two ligands is so potent and selective. All these findings might provide useful insights for developing novel and effective drugs to treat cancer, diabetes and obesity.

Insight into the molecular switch mechanism of human Rab5a from molecular dynamics simulations

Rab5a is currently a most interesting target because it is responsible for regulating the early endosome fusion in endocytosis and possibly the budding process. We utilized longtime-scale molecular dynamics simulations to investigate the internal motion of the wild-type Rab5a and its A30P mutant. It was observed that, after binding with GTP, the global flexibility of the two proteins is increasing, while the local flexibility in their sensitive sites (P-loop, switch I and II regions) is decreasing. Also, the mutation of Ala30 to Pro30 can cause notable flexibility variations in the sensitive sites. However, this kind of variations is dramatically reduced after binding with GTP. Such a remarkable feature is mainly caused by the water network rearrangements in the sensitive sites. These findings might be of use for revealing the profound mechanism of the displacements of Rab5a switch regions, as well as the mechanism of the GDP dissociation and GTP association.

Reversal of coenzyme specificity and improvement of catalytic efficiency of Pichia stipitis xylose reductase by rational site-directed mutagenesis

A major problem when xylose is used for ethanol production is the intercellular redox imbalance arising from different coenzyme specificities of xylose reductase (XR) and xylitol dehydrogenase. The residue Lys21 in XR from Pichia stipitis was subjected to site-directed mutagenesis to alter its coenzyme specificity. The N272D mutant exhibited improved catalytic efficiency when NADH was the coenzyme. Both K21A and K21A/N272D preferred NADH to NADPH, their catalytic efficiencies for NADPH were almost zero. The catalytic efficiency of K21A/N272D for NADH was almost 9-fold and 2-fold that of K21A and the wild-type enzyme, respectively. Complete reversal of coenzyme specificity toward NADH and improved catalytic efficiency were achieved.

Structural flexibility and interactions of PTP1B’s S-loop

Protein-tyrosine phosphatase 1B (PTP1B) is an attractive drug target for type II diabetes and obesity. The structural motions of its S-loop play crucial roles in WPD-loop closure that is essential for the catalytic mechanism of this protein. In the current studies, totally 20 ns molecular dynamics simulations were employed on both PTP1B and its complex with inhibitors in the explicit solution surroundings with the periodic boundary conditions in order to perform detail exam on the structural flexibility of S-loop. Together with calculating RMSD values and monitoring the distances between active site and the residues in S-loop, it is found that S-loop can move towards to active site and form a tight binding pocket for substrates upon inhibitor binding. And a hydrogen bond network rearrangement was detected in this region, which may cause the transforms of both the tree-dimensional structure and the total accessible surfaces for the residues in S loop. Additionally, the second structures of Ser201 and Gly209 have huge changes for the open system, which is not detected in close system. These findings can reveal the possible mechanism of ligand recognitions and inhibitions, further providing useful information to design novel inhibitors against PTP1B and develop new treatment for type II diabetes and obesity.

Interactions of CYP2C9 with Different Substrates and its Implications for Metabolic Mechanism

Cytochrome P450 2C9 (CYP2C9) is among most important members of the cytochrome P450 enzyme superfamily, which metabolizes many important exogenous and endogenous compounds in many species of microorganisms, plants and animals. CYP2C9 is related to the oxidative of 16% of all therapeutics in clinical use and has adverse drug effects, for example, enzyme induction and inhibition. In order to understand the metabolic mechanism of various drugs, two crystal structures of CYP2C9 have been studied, and their structure-activity relationships with the drugs of Fluoxetine, Ibuprofen, Naproxen, Suprofen, and Mefenamic acid investigated. By series of docking studies and MD simulations, the binding pockets of CYP2C9 for the five drugs are explicitly defined that will be very useful for conducting mutagenesis studies, providing insights into the metabolic mechanism, which may of relevance to the personalized drug.