| 摘要 |
A modified cereal (1->3,1->4)-beta-glucanase is produced by the method of single point substitution in a native cereal (1->3,1->4)-beta-glucanase enzyme, whereby the substitution: a) maintains enzyme specificity by conserving the active site groove of the native cereal (1->3,1->4)-beta-glucanase enzyme; and b) effects increased thermostability over the native cereal (1->3,1->4)-beta-glucanase enzyme by: i) replacing glycine by proline or alanine in helices of the cereal (1->3,1->4)-beta-glucanase enzyme, in order to stiffen the enzyme amino acid chain and reduce entropy of the unfolded enzyme; ii) attaching negatively charged residues to N-termini of helices in the native cereal (1->3,1->4)-beta-glucanase enzyme; iii) introducing ion pairs into the native cereal (1->3,1->4)-beta-glucanase enzyme, to increase binding energy in the folded enzyme; iv) replacing lysine by arginine in the cereal (1->3,1->4)-beta-glucanase enzyme, and thereby preventing lysine glycation and increasing hydrogen bonding with other parts of the enzyme; v) replacing, by glycine, an amino acid in the native cereal (1->3,1->4)-beta-glucanase enzyme in which the main chain torsion angle about the N and Calpha atoms is greater than 0°; or vi) creating cysteine pairs in the native cereal (1->3,1->4)-beta-glucanase enzyme which can form disulphide bonds across the C and N terminals.
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