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dc.contributor.authorSmith, Clyde A.
dc.contributor.authorToogood, Helen S.
dc.contributor.authorBaker, Heather M.
dc.contributor.authorDaniel, Roy M.
dc.contributor.authorBaker, Edward N.
dc.identifier.citationSmith, C.A., Toogood, H.S., Baker, H.M., Daniel, R.M. & Baker, E.N. (1999). Calcium-mediated thermostability in the subtilisin superfamily: the crystal structure of Bacillus Ak.1 protease at 1.8 å resolution. Journal of Molecular Biology, 294(4), 1027-1040.en_NZ
dc.description.abstractProteins of the subtilisin superfamily (subtilases) are widely distributed through many living species, where they perform a variety of processing functions. They are also used extensively in industry. In many of these enzymes, bound calcium ions play a key role in protecting against autolysis and thermal denaturation. We have determined the crystal structure of a highly thermostable protease from Bacillus sp. Ak.1 that is strongly stabilized by calcium. The crystal structure, determined at 1.8 Å resolution (R=0.182, Rfree=0.247), reveals the presence of four bound cations, three Ca2+ and one Na+. Two of the Ca2+ binding sites, Ca-1 and Ca-2, correspond to sites also found in thermitase and the mesophilic subtilisins. The third calcium ion, however, is at a novel site that is created by two key amino acid substitutions near Ca-1, and has not been observed in any other subtilase. This site, acting cooperatively with Ca-1, appears to give substantially enhanced thermostability, compared with thermitase. Comparisons with the mesophilic subtilisins also point to the importance of aromatic clusters, reduced hydrophobic surface and constrained N and C termini in enhancing the thermostability of thermitase and Ak.1 protease. The Ak.1 protease also contains an unusual Cys-X-Cys disulfide bridge that modifies the active site cleft geometry.en_NZ
dc.subjectcalcium bindingen_NZ
dc.subjectcrystal structureen_NZ
dc.subjectserine proteaseen_NZ
dc.subjectsubtilase familyen_NZ
dc.titleCalcium-mediated thermostability in the subtilisin superfamily: the crystal structure of Bacillus Ak.1 protease at 1.8 å resolutionen_NZ
dc.typeJournal Articleen_NZ
dc.relation.isPartOfJournal of Molecular Biologyen_NZ

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