title: Structure of a highly acidic β-lactamase from the moderate halophile Chromohalobacter sp. 560 and the discovery of a Cs(+)-selective binding site.
abstract: Environmentally friendly absorbents are needed for Sr(2+) and Cs(+), as the removal of the radioactive Sr(2+) and Cs(+) that has leaked from the Fukushima Nuclear Power Plant is one of the most important problems in Japan. Halophilic proteins are known to have many acidic residues on their surface that can provide specific binding sites for metal ions such as Cs(+) or Sr(2+). The crystal structure of a halophilic β-lactamase from Chromohalobacter sp. 560 (HaBLA) was determined to resolutions of between 1.8 and 2.9 Å in space group P31 using X-ray crystallography. Moreover, the locations of bound Sr(2+) and Cs(+) ions were identified by anomalous X-ray diffraction. The location of one Cs(+)-specific binding site was identified in HaBLA even in the presence of a ninefold molar excess of Na(+) (90 mM Na(+)/10 mM Cs(+)). From an activity assay using isothermal titration calorimetry, the bound Sr(2+) and Cs(+) ions do not significantly affect the enzymatic function of HaBLA. The observation of a selective and high-affinity Cs(+)-binding site provides important information that is useful for the design of artificial Cs(+)-binding sites that may be useful in the bioremediation of radioactive isotopes.
authors.affiliation: Quantum Beam Science Directorate, Japan Atomic Energy Agency, 2-4 Shirakata-shirane, Tokai, Ibaraki 319-1195, Japan.
authors.forename: Shigeki
authors.initials: S
authors.lastname: Arai
authors.affiliation: Quantum Beam Science Directorate, Japan Atomic Energy Agency, 2-4 Shirakata-shirane, Tokai, Ibaraki 319-1195, Japan.
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Yonezawa
authors.affiliation: Quantum Beam Science Directorate, Japan Atomic Energy Agency, 2-4 Shirakata-shirane, Tokai, Ibaraki 319-1195, Japan.
authors.forename: Nobuo
authors.initials: N
authors.lastname: Okazaki
authors.affiliation: Quantum Beam Science Directorate, Japan Atomic Energy Agency, 2-4 Shirakata-shirane, Tokai, Ibaraki 319-1195, Japan.
authors.forename: Fumiko
authors.initials: F
authors.lastname: Matsumoto
authors.affiliation: Quantum Beam Science Directorate, Japan Atomic Energy Agency, 2-4 Shirakata-shirane, Tokai, Ibaraki 319-1195, Japan.
authors.forename: Chie
authors.initials: C
authors.lastname: Shibazaki
authors.affiliation: Quantum Beam Science Directorate, Japan Atomic Energy Agency, 2-4 Shirakata-shirane, Tokai, Ibaraki 319-1195, Japan.
authors.forename: Rumi
authors.initials: R
authors.lastname: Shimizu
authors.affiliation: Quantum Beam Science Directorate, Japan Atomic Energy Agency, 2-4 Shirakata-shirane, Tokai, Ibaraki 319-1195, Japan.
authors.forename: Mitsugu
authors.initials: M
authors.lastname: Yamada
authors.affiliation: Quantum Beam Science Directorate, Japan Atomic Energy Agency, 2-4 Shirakata-shirane, Tokai, Ibaraki 319-1195, Japan.
authors.forename: Motoyasu
authors.initials: M
authors.lastname: Adachi
authors.affiliation: Quantum Beam Science Directorate, Japan Atomic Energy Agency, 2-4 Shirakata-shirane, Tokai, Ibaraki 319-1195, Japan.
authors.forename: Taro
authors.initials: T
authors.lastname: Tamada
authors.affiliation: Saga Prefectural Regional Industry Support Center, Kyushu Synchrotron Light Research Center, 8-7 Yayoigaoka, Tosu, Saga 841-0005, Japan.
authors.forename: Masahide
authors.initials: M
authors.lastname: Kawamoto
authors.affiliation: Applied and Molecular Microbiology, Faculty of Agriculture, Kagoshima University, 1-21-24 Korimoto, Kagoshima 890-0065, Japan.
authors.forename: Hiroko
authors.initials: H
authors.lastname: Tokunaga
authors.affiliation: Applied and Molecular Microbiology, Faculty of Agriculture, Kagoshima University, 1-21-24 Korimoto, Kagoshima 890-0065, Japan.
authors.forename: Matsujiro
authors.initials: M
authors.lastname: Ishibashi
authors.affiliation: Quantum Beam Science Directorate, Japan Atomic Energy Agency, 2-4 Shirakata-shirane, Tokai, Ibaraki 319-1195, Japan.
authors.forename: Michael
authors.initials: M
authors.lastname: Blaber
authors.affiliation: Applied and Molecular Microbiology, Faculty of Agriculture, Kagoshima University, 1-21-24 Korimoto, Kagoshima 890-0065, Japan.
authors.forename: Masao
authors.initials: M
authors.lastname: Tokunaga
authors.affiliation: Quantum Beam Science Directorate, Japan Atomic Energy Agency, 2-4 Shirakata-shirane, Tokai, Ibaraki 319-1195, Japan.
authors.forename: Ryota
authors.initials: R
authors.lastname: Kuroki
mesh_terms: D001665:Binding Sites; D002586:Cesium / Q000737:chemistry*; D055353:Chromohalobacter / Q000201:enzymology*; D018360:Crystallography, X-Ray; D011485:Protein Binding; D013324:Strontium / Q000737:chemistry; D001618:beta-Lactamases / Q000737:chemistry*
chemical_list: D002586:Cesium; D001618:beta-Lactamases; D013324:Strontium
keywords: Chromohalobacter sp.; Cs+ binding; Sr2+ binding; β-lactamase