Multi-site substrate binding and interplay in barley alpha-amylase 1 |
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Authors: | Nielsen Morten Munch Seo Eun-Seong Bozonnet Sophie Aghajari Nushin Robert Xavier Haser Richard Svensson Birte |
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Affiliation: | Enzyme and Protein Chemistry, Department of Systems Biology, Technical University of Denmark, S?ltofts Plads, Lyngby, Denmark. |
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Abstract: | Certain starch hydrolases possess secondary carbohydrate binding sites outside of the active site, suggesting that multi-site substrate interactions are functionally significant. In barley alpha-amylase both Tyr380, situated on a remote non-catalytic domain, and Tyr105 in subsite -6 of the active site cleft are principal carbohydrate binding residues. The dual active site/secondary site mutants Y105A/Y380A and Y105A/Y380M show that each of Tyr380 and Tyr105 is important, albeit not essential for binding, degradation, and multiple attack on polysaccharides, while Tyr105 predominates in oligosaccharide hydrolysis. Additional delicate structure/function relationships of the secondary site are uncovered using Y380A/H395A, Y380A, and H395A AMY1 mutants. |
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Keywords: | Carbohydrate binding surface site Starch granules β-cyclodextrin Site-directed mutagenesis Multiple attack Crystallography |
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