Amino acid sequences of two high-potential iron-sulfur proteins (HiPIPs) from the moderately halophilic purple phototrophic bacterium, Rhodospirillumsalinarum

The amino acid sequences of two very different high-potential iron-sulfur p rotein (HiPIP) isozymes have been determined from the moderately halophilic purple phototrophic bacterium, Rhodospirillum salinarum. Iso-1 HiPIP, whic h is monomeric and contains 57 amino acid residues, is most similar to the Thiobacillus ferrooxidans iron-oxidizing enzyme (45% identity and a 6-resid ue deletion). On the other hand, iso-2 HiPIP, which is isolated as an oligo mer, contains a peptide chain with 54 amino acid residues. It is the smalle st reported to date and is only 31% identical to iso-1 HiPIP. A massive del etion of 17 residues is found at the N-terminus, such that only 2 residues remain prior to the first cysteine. Iso-2 HiPIP also has a 12-residue inser tion and a 5-residue deletion. Prior to this study, there were only 2 absol utely conserved residues (Tyr 19 and Gly 75, Chromatium numbering) in addit ion to the 4 iron-sulfur cluster binding cysteine residues among the 13 HiP IPs sequenced to date. We found that Tyr 19 is absent in iso-2 HiPIP along with the entire N-terminal loop. Moreover, Gay 75 is substituted in both R. salinarum HiPIPs. These characteristics make the R. salinarum HiPIPs, and especially iso-2, the most divergent yet characterized. (C) 1999 Academic P ress