br Results and discussion GSTP is

Results and discussion GSTP1 is a Phase II cytoprotective and detoxifying enzyme. Due to its role in the detoxification of numerous endogenous and exogenous chemical agents (with electrophilic functional groups), individuals with Ile105Val mutation in this gene show enhanced risk of atopic disorder (Hoskins et al., 2013), neuropathy (Kanai et al., 2010, Grisold et al., 2012) and cancer (Rybicki et al., 2006, Vlaykova et al., 2007). Impact of rs1695 polymorphism in the hydrophobic catalytic site, leading to varied substrate binding could seriously affect the detoxicating as well as drug metabolism capability and hamper its positive effect in the individual. One reason is that hydrophobicity decreases when Ile is substituted with Val as the van der Waal's volume of Ile is 124Å3 and that of Val is 105Å3 (Creighton, 1993). The major objective of the current work was to investigate to what extent the polymorphism at position 105 of human GSTP1 affects the binding of the enzyme with various compounds having diverse drug properties but mostly targeting GSTP1 for cancer treatment. Docking/dynamics simulation of the WT and variant polymorphs is a long established method for interpreting changes in proteins at a single residue scale. Use of this methodology for gene-polymorphisms, their bound ligand interactions and g proteins landscape is a quick and useful method for obtaining rapid insights into deleterious functionality. A standardized docking workflow was employed that divided docking into a series of protocols and a comparison of binding energies of WT and variant GSTP1 was attempted to differentiate conformational changes upon substrate binding to the hydrophobic catalytic site residues of this antioxidant protein. Docking simulation basically entails a search for discovering favoured orientation and the conformational space accessible to the system alongside a force field to assess the energy of each complex. Empirical free energy force fields outline simple functional formulae for ligand–protein interactions while semi-empirical free energy force fields pool traditional molecular mechanics force fields using empirical weights and/or functional forms (Huey et al., 2007, Miceli et al., 2013). MOE was used for docking purpose, with London dG parameter employed for scoring of functions and Amber, an empirical force field for refinement of docked complexes. Affinity dG was used for rescoring. Residues forming hydrophobic and hydrogen bonding interactions with all of the docked substrates were dissimilar among the WT and variant GSTP1 (Table 2). GSTP1 protein consists of two subunits, both of them allied by a 2-fold symmetry axis. Each subunit comprises of an active site is divided into two sub parts, a glutathione binding region and hydrophobic substrate binding region (Mannervik et al., 1978). N-terminal domain encompasses one-third of the protein, enclosing glutathione binding region. It also consists of a conserved βαβαββα motif. C-terminal domain is entirely comprised of α-helices and encompasses hydrophobic catalytic site, along with a loop originating from the N-terminal domain (Dirr et al., 1994, Armstrong, 1997, Johansson, 2002). Chemical compounds were docked into the hydrophobic catalytic site. A hydrophobic to polar residue shift was observed in busulfan interaction with WT and variant GSTP1 polymorph, respectively. Arene cation (or cation- π) interactions were lost in the binding complex, upon mutation induction. These types of interactions illustrate non-covalent bonding between a monopole (cation) and a quadrupole (π system). Solution-phase values are of same magnitude as hydrogen bonds and salt bridges alongside substantial bonding energies. These interactions have a vital role in molecular recognition as well as enzyme catalysis (Dougherty and Ma, 1997). These interactions (Arene cation interactions of positive quadrupole moment aromatics) were also lost in carbocisteine, carboplatin clomipramine and chlorambucil upon Ile105Val mutation induction in GSTP1, whereas, in etoposide and oxaliplatin, a gain of arene cation interactions depicting positive quadrupole moment aromatics was observed upon mutation introduction. Likewise, a loss and gain of electron acceptance status of the compounds was observed after generation of mutation in GSTP1. Shift in the positively charged and negatively charged catalytic site bonding residues was also detected. Binding energy profile showed a consistency in the trend, decreasing with variant polymorph tethering for all compounds.