title: The 2.0A resolution structure of the catalytic portion of a cyanobacterial membrane-bound manganese superoxide dismutase.
abstract: Cyanobacteria are shown to be unique in containing membrane-bound manganese superoxide dismutases (MnSOD). They are homodimeric type 2 membrane proteins that protect this phototrophic organism against oxidative stress. We have determined, for the first time, the 2.0A resolution structure of the catalytic portion of the MnSOD from the filamentous cyanobacterium Anabaena PCC 7120. Within each subunit, both the N-terminal helical hairpin (His94 and His145) and the C-terminal alpha/beta domain (His232 and Asp228) contribute ligands to the catalytic manganese site. Together with a water or hydroxide ion (OH(x)) a five-coordinated trigonal bipyramidal geometry is formed, with OH(x) and His90 forming the axial ligands and manganese shifted out of the equatorial plane in the direction of OH(x). The ligands including OH(x) are tightly constrained by hydrogen bonding with surrounding residues either from the same monomer (Tyr98, Asn144, Trp194, Gln213, Val229, Trp230) or from the neighbouring subunit (Glu231, Tyr235). This underlines the important role of the symmetric dimeric structure of MnSODs in contributing elements to both the active site and the substrate funnel. The Mn cdots, three dots, centered Mn distance (18.4A) is bridged by the hydrogen-bonded His232 of one monomer with Glu231 of the other monomer. A detailed discussion of the structure, a comparison with known structures of soluble MnSODs as well as a model of the cyanobacterial membrane-bound MnSOD is presented.
authors.affiliation: Max-Planck-Institut für Biochemie/Abt. Strukturforschung, Am Klopferspitz 18a, D-82152 Martinsried/Planegg, Munich, Germany.
authors.forename: Werner
authors.initials: W
authors.lastname: Atzenhofer
authors.forename: Günther
authors.initials: G
authors.lastname: Regelsberger
authors.forename: Uwe
authors.initials: U
authors.lastname: Jacob
authors.forename: Günter
authors.initials: G
authors.lastname: Peschek
authors.forename: Paul
authors.initials: P
authors.lastname: Furtmüller
authors.forename: Robert
authors.initials: R
authors.lastname: Huber
authors.forename: Christian
authors.initials: C
authors.lastname: Obinger
mesh_terms: D000595:Amino Acid Sequence; D017033:Anabaena / Q000201:enzymology*; D001483:Base Sequence; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D017931:DNA Primers; D004591:Electrophoresis, Polyacrylamide Gel; D008565:Membrane Proteins / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013482:Superoxide Dismutase / Q000737:chemistry* / Q000378:metabolism
chemical_list: D017931:DNA Primers; D008565:Membrane Proteins; D011994:Recombinant Proteins; D013482:Superoxide Dismutase