1q6f
Crystal Structure of Soybean Beta-Amylase Mutant (E178Y) with Increased pH Optimum at pH 7.1
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OverviewOverview
Comparison of the architecture around the active site of soybean, beta-amylase and Bacillus cereus beta-amylase showed that the hydrogen, bond networks (Glu380-(Lys295-Met51) and Glu380-Asn340-Glu178) in soybean, beta-amylase around the base catalytic residue, Glu380, seem to contribute, to the lower pH optimum of soybean beta-amylase. To convert the pH optimum, of soybean beta-amylase (pH 5.4) to that of the bacterial type enzyme (pH, 6.7), three mutants of soybean beta-amylase, M51T, E178Y, and N340T, were, constructed such that the hydrogen bond networks were removed by, site-directed mutagenesis. The kinetic analysis showed that the pH optimum, of all mutants shifted dramatically to a neutral pH (range, from 5.4 to, 6.0-6.6). The Km values of the mutants were almost the same as that of, soybean beta-amylase except in the case of M51T, while the Vmax values of, all mutants were low compared with that of soybean beta-amylase. The, crystal structure analysis of the wild type-maltose and mutant-maltose, complexes showed that the direct hydrogen bond between Glu380 and Asn340, was completely disrupted in the mutants M51T, E178Y, and N340T. In the, case of M51T, the hydrogen bond between Glu380 and Lys295 was also, disrupted. These results indicated that the reduced pKa value of Glu380 is, stabilized by the hydrogen bond network and is responsible for the lower, pH optimum of soybean beta-amylase compared with that of the bacterial, beta-amylase.
About this StructureAbout this Structure
1Q6F is a Single protein structure of sequence from Glycine max with SO4 as ligand. Active as Beta-amylase, with EC number 3.2.1.2 Full crystallographic information is available from OCA.
ReferenceReference
Structural and enzymatic analysis of soybean beta-amylase mutants with increased pH optimum., Hirata A, Adachi M, Sekine A, Kang YN, Utsumi S, Mikami B, J Biol Chem. 2004 Feb 20;279(8):7287-95. Epub 2003 Nov 24. PMID:14638688
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