title: Giardia lamblia encodes a functional flavohemoglobin.
abstract: Giardia lamblia is a pathogenic protist that infects the small intestine of mammals. As a facultative anaerobe, Giardia obtains all of its energy by substrate-level phosphorylation, lacks a functioning respiratory chain, and is not thought to require heme. However, sequencing of the G. lamblia genome has identified several putative heme proteins, one of which shares high sequence similarity to flavohemoglobins found in bacteria and some single-celled eukaryotes. We have cloned and characterized the functional properties of the G. lamblia flavohemoglobin. The protein is monomeric, binds heme and flavin adenine dinucleotide, and exhibits similar behavior to known flavohemoglobins, including NADH and NADPH oxidase activity, which is stimulated by addition of the nitric oxide donor DEA/NO. Based on its structural and functional properties, the likely role of this protein is to protect Giardia against oxygen, nitric oxide, or both. The presence of a Giardia gene encoding a functional heme protein raises questions on how this organism acquires the heme cofactor, which hitherto have been unexplored.
authors.affiliation: Department of Chemistry, Trent University, 1600 West Bank Drive, Peterborough, ON, Canada K9J 7B8. srafferty@trentu.ca
authors.forename: Steven
authors.initials: S
authors.lastname: Rafferty
authors.forename: Betty
authors.initials: B
authors.lastname: Luu
authors.forename: Raymond E
authors.initials: RE
authors.lastname: March
authors.forename: Janet
authors.initials: J
authors.lastname: Yee
mesh_terms: D000595:Amino Acid Sequence; D005182:Flavin-Adenine Dinucleotide / Q000378:metabolism; D005815:Genetic Code; D016829:Giardia lamblia / Q000235:genetics / Q000378:metabolism*; D006418:Heme / Q000378:metabolism; D006420:Hemeproteins / Q000737:chemistry* / Q000235:genetics; D008969:Molecular Sequence Data; D017434:Protein Structure, Tertiary
chemical_list: D006420:Hemeproteins; D005182:Flavin-Adenine Dinucleotide; D006418:Heme