The O2-scavenging flavodiiron protein in the human parasite Giardia intestinalis.
The flavodiiron proteins (FDP) are widespread among strict or facultative anaerobic prokaryotes, where they are involved in the response to nitrosative and/or oxidative stress. Unexpectedly, FDPs were fairly recently identified in a restricted group of microaerobic protozoa, including Giardia intestinalis, the causative agent of the human infectious disease giardiasis. The FDP from Giardia was expressed, purified, and extensively characterized by x-ray crystallography, stopped-flow spectroscopy, respirometry, and NO amperometry. Contrary to flavorubredoxin, the FDP from Escherichia coli, the enzyme from Giardia has high O(2)-reductase activity (>40 s(-1)), but very low NO-reductase activity (approximately 0.2 s(-1)); O(2) reacts with the reduced protein quite rapidly (milliseconds) and with high affinity (K(m) < or = 2 microM), producing H(2)O. The three-dimensional structure of the oxidized protein determined at 1.9A resolution shows remarkable similarities with prokaryotic FDPs. Consistent with HPLC analysis, the enzyme is a dimer of dimers with FMN and the non-heme di-iron site topologically close at the monomer-monomer interface. Unlike the FDP from Desulfovibrio gigas, the residue His-90 is a ligand of the di-iron site, in contrast with the proposal that ligation of this histidine is crucial for a preferential specificity for NO. We propose that in G. intestinalis the primary function of FDP is to efficiently scavenge O(2), allowing this microaerobic parasite to survive in the human small intestine, thus promoting its pathogenicity.
Di Matteo
Adele
A
Department of Biochemical Sciences, CNR Institute of Molecular Biology and Pathology and Istituto Pasteur-Fondazione Cenci Bolognetti, Sapienza, University of Rome, Rome I-00185, Italy.
Scandurra
Francesca Maria
FM
Testa
Fabrizio
F
Forte
Elena
E
Sarti
Paolo
P
Brunori
Maurizio
M
Giuffrè
Alessandro
A
D000818:Animals; D002851:Chromatography, High Pressure Liquid; D018360:Crystallography, X-Ray; D005420:Flavoproteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D016829:Giardia lamblia / Q000378:metabolism*; D007501:Iron / Q000378:metabolism*; D008958:Models, Molecular; D010100:Oxygen / Q000378:metabolism*; D011487:Protein Conformation; D013057:Spectrum Analysis
D005420:Flavoproteins; D007501:Iron; D010100:Oxygen