title: Fluorescence studies on the stability, flexibility and substrate-induced conformational changes of acetate kinases from psychrophilic and mesophilic bacteria.
abstract: The acetate kinase from the Antarctic psychrophilic Shewanella sp. AS-11 (SAK) has a significantly higher catalytic efficiency at low temperatures when compared with that from mesophilic Escherichia coli K-12 (EAK). To examine the stability and conformational flexibility of SAK and EAK, steady state intrinsic fluorescence studies were performed. EAK contains only one Trp at a position 46, while SAK contains two Trps at positions 46 and 388. From the fluorescence emission spectra, quenching with acrylamide, Cs(+) and I(-) at different temperatures and denaturation with guanidine-HCl, it was revealed that the SAK bears more flexible and unstable structure than that of EAK. Substrate-induced conformational changes reflect that SAK reached transition state through more conformational changes than EAK. In combination of our thermodynamic studies on the enzymatic reaction and present research findings, it can be concluded that these structural features of SAK may contribute to its high catalytic efficiency at low temperatures.
authors.affiliation: Department of Applied Biochemistry and Food Science, Saga University, 1-Honjo-machi, Saga, Japan. makashemsa@gmail.com
authors.forename: Md Abul Kashem
authors.initials: MA
authors.lastname: Tang
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Motoshima
authors.forename: Keiichi
authors.initials: K
authors.lastname: Watanabe
mesh_terms: D000084:Acetate Kinase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D004795:Enzyme Stability; D048168:Escherichia coli K12 / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D007700:Kinetics; D008969:Molecular Sequence Data; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D020592:Shewanella / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics; D013379:Substrate Specificity
chemical_list: D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D000084:Acetate Kinase