title: The Phylogeny and Active Site Design of Eukaryotic Copper-only Superoxide Dismutases.
abstract: In eukaryotes the bimetallic Cu/Zn superoxide dismutase (SOD) enzymes play important roles in the biology of reactive oxygen species by disproportionating superoxide anion. Recently, we reported that the fungal pathogen Candida albicans expresses a novel copper-only SOD, known as SOD5, that lacks the zinc cofactor and electrostatic loop (ESL) domain of Cu/Zn-SODs for substrate guidance. Despite these abnormalities, C. albicans SOD5 can disproportionate superoxide at rates limited only by diffusion. Here we demonstrate that this curious copper-only SOD occurs throughout the fungal kingdom as well as in phylogenetically distant oomycetes or "pseudofungi" species. It is the only form of extracellular SOD in fungi and oomycetes, in stark contrast to the extracellular Cu/Zn-SODs of plants and animals. Through structural biology and biochemical approaches we demonstrate that these copper-only SODs have evolved with a specialized active site consisting of two highly conserved residues equivalent to SOD5 Glu-110 and Asp-113. The equivalent positions are zinc binding ligands in Cu/Zn-SODs and have evolved in copper-only SODs to control catalysis and copper binding in lieu of zinc and the ESL. Similar to the zinc ion in Cu/Zn-SODs, SOD5 Glu-110 helps orient a key copper-coordinating histidine and extends the pH range of enzyme catalysis. SOD5 Asp-113 connects to the active site in a manner similar to that of the ESL in Cu/Zn-SODs and assists in copper cofactor binding. Copper-only SODs are virulence factors for certain fungal pathogens; thus this unique active site may be a target for future anti-fungal strategies.
authors.affiliation: From the Department of Biochemistry and Molecular Biology, Johns Hopkins University Bloomberg School of Public Health, Baltimore, Maryland 21205.
authors.forename: Ryan L
authors.initials: RL
authors.lastname: Peterson
authors.affiliation: Department of Biological Sciences, St. Mary's University, San Antonio, Texas 78228, Department of Biochemistry, University of Texas Health Science Center, San Antonio, Texas 78229.
authors.forename: Ahmad
authors.initials: A
authors.lastname: Galaleldeen
authors.affiliation: Department of Biological Sciences, St. Mary's University, San Antonio, Texas 78228.
authors.forename: Johanna
authors.initials: J
authors.lastname: Villarreal
authors.affiliation: Department of Biochemistry, University of Texas Health Science Center, San Antonio, Texas 78229.
authors.forename: Alexander B
authors.initials: AB
authors.lastname: Taylor
authors.affiliation: Chemistry Department, Brookhaven National Laboratories, Upton, New York 11973-5000, and.
authors.forename: Diane E
authors.initials: DE
authors.lastname: Cabelli
authors.affiliation: Department of Biochemistry, University of Texas Health Science Center, San Antonio, Texas 78229, Department of Veterans Affairs, Geriatric Research, Education, and Clinical Center, South Texas Veterans Health Care System, San Antonio, Texas 78229.
authors.forename: P John
authors.initials: PJ
authors.lastname: Hart
authors.affiliation: From the Department of Biochemistry and Molecular Biology, Johns Hopkins University Bloomberg School of Public Health, Baltimore, Maryland 21205, vculott1@jhu.edu.
authors.forename: Valeria C
authors.initials: VC
authors.lastname: Culotta
mesh_terms: D002176:Candida albicans / Q000201:enzymology* / Q000235:genetics; D002384:Catalysis; D003300:Copper / Q000737:chemistry* / Q000378:metabolism; D005656:Fungal Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D009868:Oomycetes / Q000201:enzymology / Q000235:genetics; D013482:Superoxide Dismutase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D015032:Zinc / Q000737:chemistry* / Q000378:metabolism
chemical_list: D005656:Fungal Proteins; D003300:Copper; D013482:Superoxide Dismutase; D015032:Zinc
keywords: copper; enzyme; fungi; superoxide dismutase (SOD); superoxide ion; x-ray crystallography