Flavohemoglobin and nitric oxide detoxification in the human protozoan parasite Giardia intestinalis.
Flavohemoglobins (flavoHbs), commonly found in bacteria and fungi, afford protection from nitrosative stress by degrading nitric oxide (NO) to nitrate. Giardia intestinalis, a microaerophilic parasite causing one of the most common intestinal human infectious diseases worldwide, is the only pathogenic protozoon as yet identified coding for a flavoHb. By NO amperometry we show that, in the presence of NADH, the recombinant Giardia flavoHb metabolizes NO with high efficacy under aerobic conditions (TN=116+/-10s(-1) at 1microM NO, T=37 degrees C). The activity is [O(2)]-dependent and characterized by an apparent K(M,O2)=22+/-7microM. Immunoblotting analysis shows that the protein is expressed at low levels in the vegetative trophozoites of Giardia; accordingly, these cells aerobically metabolize NO with low efficacy. Interestingly, in response to nitrosative stress (24-h incubation with 5mM nitrite) flavoHb expression is enhanced and the trophozoites thereby become able to metabolize NO efficiently, the activity being sensitive to both cyanide and carbon monoxide. The NO-donors S-nitrosoglutathione (GSNO) and DETA-NONOate mimicked the effect of nitrite on flavoHb expression. We propose that physiologically flavoHb contributes to NO detoxification in G. intestinalis.
Mastronicola
Daniela
D
Department of Biochemical Sciences, CNR Institute of Molecular Biology and Pathology and Istituto Pasteur - Fondazione Cenci Bolognetti, Sapienza University of Rome, I-00185 Rome, Italy.
Testa
Fabrizio
F
Forte
Elena
E
Bordi
Eugenio
E
Pucillo
Leopoldo Paolo
LP
Sarti
Paolo
P
Giuffrè
Alessandro
A
D000332:Aerobiosis; D016829:Giardia lamblia / Q000187:drug effects / Q000378:metabolism*; D006454:Hemoglobins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D009243:NAD / Q000378:metabolism; D009569:Nitric Oxide / Q000378:metabolism*; D020030:Nitric Oxide Donors / Q000494:pharmacology; D009603:Nitroso Compounds / Q000494:pharmacology; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D026422:S-Nitrosoglutathione / Q000494:pharmacology
D006454:Hemoglobins; D020030:Nitric Oxide Donors; D009603:Nitroso Compounds; D011994:Recombinant Proteins; D009243:NAD; C094210:2,2'-(hydroxynitrosohydrazono)bis-ethanamine; D009569:Nitric Oxide; D026422:S-Nitrosoglutathione