The noncatalytic triad of alpha-amylases: a novel structural motif involved in conformational stability |
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Authors: | Marx Jean-Claude Poncin Johan Simorre Jean-Pierre Ramteke Pramod W Feller Georges |
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Institution: | Laboratory of Biochemistry, University of Liège, Liège, Sart-Tilman, Belgium. |
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Abstract: | Chloride-activated alpha-amylases contain a noncatalytic triad, independent of the glycosidic active site, perfectly mimicking the catalytic triad of serine-proteases and of other active serine hydrolytic enzymes. Mutagenesis of Glu, His, and Ser residues in various alpha-amylases shows that this pattern is a structural determinant of the enzyme conformation that cannot be altered without losing the intrinsic stability of the protein. (1)H-(15)N NMR spectra of a bacterial alpha-amylase reveal proton signals that are identical with the NMR signature of catalytic triads and especially a deshielded proton involving a protonated histidine and displaying properties similar to that of a low barrier hydrogen bond. It is proposed that the H-bond between His and Glu of the noncatalytic triad is an unusually strong interaction, responsible for the observed NMR signal and for the weak stability of the triad mutants. Furthermore, a stringent template-based search of the Protein Data Bank demonstrated that this motif is not restricted to alpha-amylases, but is also found in 80 structures from 33 different proteins, amongst which SH2 domain-containing proteins are the best representatives. |
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Keywords: | α‐amylase protease catalytic triad protein stability low barrier hydrogen bond |
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