Desulfovibrio gigas neelaredoxin - A novel superoxide dismutase integratedin a putative oxygen sensory operon of an anaerobe

Neelaredoxin, a small non-heme blue iron protein from the sulfate-reducing bacterium Desulfovibrio gigas [Chen, L., Sharma, P., LeGall, J., Mariano, A .M., Teixeira M. and Xavier, A.V. (1994) Eur. J. Biochem. 226, 613-618] is shown to be encoded by a polycistronic unit which contains two additional o pen reading frames (ORF-1 and ORF-2) coding for chemotaxis-like proteins. O RF-I has domains highly homologous with those structurally and functionally important in methyl-accepting chemotaxis proteins, including two putative transmembrane helices, potential methylation sites and the interaction doma in with CheW proteins. Interestingly, ORF-2 encodes a protein having homolo gies with CheW proteins. Neelaredoxin is also shown to have significant superoxide dismutase activit y (1200 U.mg(-1)), making it a novel type of iron superoxide dismutase. Ana lysis of genomic data shows that neelaredoxin-like putative polypeptides ar e present in strict anaerobic archaea, suggesting that this is a primordial superoxide dismutase. The three proteins encoded in this operon may be inv olved in the oxygen-sensing mechanisms of this anaerobic bacterium, indicat ing a possible transcriptional mechanism to sense and respond to potential stress agents.