title: Elucidating modes of activation and herbicide resistance by sequence assembly and molecular modelling of the Acetolactate synthase complex in sugarcane.
abstract: Acetolactate synthase (ALS) catalyzes the first portion of the biosynthetic pathway leading to the generation of branched-chain amino acids. As such it is essential for plant health and is a major target for herbicides. ALS is a very poorly characterized molecule in sugarcane. The enzyme is activated and inhibited by a regulatory subunit (known as VAT1 in plants) whose mode of action is entirely unknown. Using Saccharum halepense as a template we have assembled the ALS gene of sugarcane (Saccharum hybrid) and have modelled the structure of ALS based on an Arabidopsis template (the first ALS model for a monocot). We have also assembled the ALS regulatory proteins (VAT1 and VAT2) from sugarcane and show that VAT2 is specific to true grasses. Employing a bacterial model, we have generated a structural model for VAT1, which explains why the separate domains of the proteins bind to either leucine or valine but not both. Using co-evolution studies we have determined molecular contacts by which we modelled the docking of VAT1 to ALS. In conclusion, we demonstrate how the binding of VAT1 to ALS activates ALS and show how VAT1 can also confer feedback inhibition to ALS. We validate our ALS model against biochemical data and employ this model to explain the function of a novel herbicide binding mutant in sugarcane.
authors.affiliation: South African Sugarcane Research Institute, 170 Flanders Drive, Private Bag X02, Mount Edgecombe, Durban 4300, South Africa; School of Life Sciences, College of Agriculture, Engineering and Science, University of Kwa-Zulu Natal, Private Bag X54001, Durban 4000, South Africa. Electronic address: dyfed.evans@sugar.org.za.
authors.forename: Dyfed
authors.initials: D
authors.lastname: Lloyd Evans
authors.affiliation: South African Sugarcane Research Institute, 170 Flanders Drive, Private Bag X02, Mount Edgecombe, Durban 4300, South Africa; School of Life Sciences, College of Agriculture, Engineering and Science, University of Kwa-Zulu Natal, Private Bag X54001, Durban 4000, South Africa.
authors.forename: Shailesh Vinay
authors.initials: SV
authors.lastname: Joshi
mesh_terms: D000095:Acetolactate Synthase / Q000737:chemistry*; D000596:Amino Acids / Q000737:chemistry; D020134:Catalytic Domain; D003001:Cloning, Molecular; D003198:Computer Simulation; D017343:Genes, Plant; D053209:Herbicide Resistance; D006540:Herbicides / Q000633:toxicity*; D007700:Kinetics; D008958:Models, Molecular; D062105:Molecular Docking Simulation; D010802:Phylogeny; D010940:Plant Proteins / Q000737:chemistry; D011485:Protein Binding; D012441:Saccharomyces cerevisiae / Q000201:enzymology; D031786:Saccharum / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics; D020539:Sequence Analysis, Protein
chemical_list: D000596:Amino Acids; D006540:Herbicides; D010940:Plant Proteins; D000095:Acetolactate Synthase
keywords: Acetolactate synthase; Molecular modelling; Sequence assembly; VAT1 activation; VAT1 inhibition