title: Insights into the structure-function relationship of disease resistance protein HCTR in maize (Zea mays L.): a computational structural biology approach.
abstract: The disease resistance gene Hm1 of maize encodes a NADPH-dependent reductase enzyme, HC-toxin reductase (HCTR) that detoxifies the HC toxin secreted by the race specific fungus Cochliobolus carbonum race 1. HCTR enzyme shares 29.6% sequence identity with dihydroflavonol reductase (DFR) of grape, a key enzyme involved in flavonoid biosynthesis. Here we report the comparative modelling, molecular dynamics simulation and docking studies to explain the structure-function relationship and the mode of cofactor (NADPH) binding in HCTR enzyme at the molecular level. The nucleotide binding domain of modelled HCTR adopts a classic Rossmann fold and possesses a consensus glycine rich GxGxxG motif. Molecular simulation studies suggested that HCTR model retained stability throughout the simulation in aqueous solution. HCTR model showed considerable structural identities with the cofactor binding site of DFR, but significant difference in the catalytic site might be the reason of functional divergence between these families of proteins. Similarly electrostatic surface potential analysis of both HCTR and DFR revealed profound variations in the charge distribution over the substrate binding site, which can be correlated with the sequence variability and may suggest distinct substrate-binding patterns and differences in the catalytic mechanism. Docking results indicated Phe19, Gly21, Arg40, Thr90, Gly208, Arg218, Glu221 and Thr222 are important residues for cofactor (NADPH) binding through strong hydrogen bonding and electrostatic interactions. Alanine scanning and analysis of docking energies of mutant proteins suggested that Phe19, and Arg40 are two critical residues for the cofactor binding. The result from the present study is expected to pave the way for exploration of similar genes in other economically important crop varieties.
authors.affiliation: Agri-Bioinformatics Promotion Programme, Department of Agricultural Biotechnology, Assam Agricultural University, Jorhat 785013, Assam, India; Department of Life Science and Bioinformatics, Assam University, Silchar 788011, Assam, India.
authors.forename: Budheswar
authors.initials: B
authors.lastname: Dehury
authors.forename: Mousumi
authors.initials: M
authors.lastname: Sahu
authors.forename: Mahesh Chandra
authors.initials: MC
authors.lastname: Patra
authors.forename: Kishore
authors.initials: K
authors.lastname: Sarma
authors.forename: Jagajjit
authors.initials: J
authors.lastname: Sahu
authors.forename: Priyabrata
authors.initials: P
authors.lastname: Sen
authors.forename: Mahendra Kumar
authors.initials: MK
authors.lastname: Modi
authors.forename: Manabendra Dutta
authors.initials: MD
authors.lastname: Choudhury
authors.forename: Madhumita
authors.initials: M
authors.lastname: Barooah
mesh_terms: D000595:Amino Acid Sequence; D060467:Disease Resistance; D008958:Models, Molecular; D062105:Molecular Docking Simulation; D056004:Molecular Dynamics Simulation; D008969:Molecular Sequence Data; D015394:Molecular Structure; D009249:NADP / Q000737:chemistry / Q000378:metabolism; D010456:Peptides, Cyclic / Q000737:chemistry / Q000378:metabolism; D010940:Plant Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D011487:Protein Conformation; D016415:Sequence Alignment; D055672:Static Electricity; D013329:Structure-Activity Relationship; D003313:Zea mays / Q000235:genetics / Q000378:metabolism
chemical_list: D010456:Peptides, Cyclic; D010940:Plant Proteins; D009249:NADP; C037654:HC toxin
keywords: Cofactor; Dihydroflavonol reductase; Disease resistant; HC-toxin reductase; Rossmann fold