Characterization of a blue-copper protein, auracyanin, of the filamentous anoxygenic phototrophic bacterium Roseiflexus castenholzii

A blue-copper protein auracyanin of the filamentous anoxygenic phototroph Roseiflexus castenholzii was purified and characterized. Genomic sequence analysis showed that R. castenholzii has only one auracyanin, whereas Chloroflexus aurantiacus is known to have two auracyanins, A and B. Absorption spectrum of the Roseiflexus auracyanin was similar to that of auracyanin B of C. aurantiacus. On the other hand, ESR spectrum of the Roseiflexus auracyanin resembles that of auracyanin A of C. aurantiacus. These results suggest that the blue-copper protein auracyanin from R. castenholzii shares features with each of auracyanin A and B. Amino acid sequence alignment of auracyanins from filamentous anoxygenic phototrophs also demonstrated the chimeral feature of the primary structure of the Roseiflexus auracyanin, i.e., auracyanin A-like amino-terminal characteristics and auracyanin B-like one-residue spacing at the Cu-binding loop in the carboxyl-terminus.