Intrapeptide sequence homology in rubrerythrin from Desulfovibrio vulgaris: identification of potential ligands to the diiron site.

Two regions in the amino acid sequence of the 21.5 kDa subunit of rubrerythrin from Desulfovibrio vulgaris (Hildenborough) are shown to be homologous. Rubrerythrin contains a non-heme, non-sulfur diiron site, and the internally homologous regions share homology with at least one proposed iron binding region of the component A alpha subunit of methane monooxygenase, which also contains a non-heme, non-sulfur diiron site. Comparison of the rubrerythrin sequences with those of the B2 subunit of E. coli ribonucleotide reductase, whose diiron site ligands have been identified, suggests that two glutamate and two histidine residues at positions 53, 56, 129, and 131 within the rubrerythrin sequence furnish ligands to the diiron site. A pair of EXXH sequences appears to represent a diiron binding motif in all three aforementioned proteins. No propene monooxygenase activity was detected with rubrerythrin using the assay designed to test activity of methane monooxygenase component A in the absence of other protein components.