Occurrence and sequence of Sphaeroides Heme Protein and diheme cytochrome C in purple photosynthetic bacteria in the family Rhodobacteraceae.
BACKGROUND
Sphaeroides Heme Protein (SHP) was discovered in the purple photosynthetic bacterium, Rhodobacter sphaeroides, and is the only known c-type heme protein that binds oxygen. Although initially not believed to be widespread among the photosynthetic bacteria, the gene has now been found in more than 40 species of proteobacteria and generally appears to be regulated. Rb. sphaeroides is exceptional in not having regulatory genes associated with the operon. We have thus analyzed additional purple bacteria for the SHP gene and examined the genetic context to obtain new insights into the operon, its distribution, and possible function.


RESULTS
We found SHP in 9 out of 10 strains of Rb. sphaeroides and in 5 out of 10 purple photosynthetic bacterial species in the family Rhodobacteraceae. We found a remarkable similarity within the family including the lack of regulatory genes. Within the proteobacteria as a whole, SHP is part of a 3-6 gene operon that includes a membrane-spanning diheme cytochrome b and one or two diheme cytochromes c. Other genes in the operon include one of three distinct sensor kinase - response regulators, depending on species, that are likely to regulate SHP.


CONCLUSIONS
SHP is not as rare as generally believed and has a role to play in the photosynthetic bacteria. Furthermore, the two companion cytochromes along with SHP are likely to function as an electron transfer pathway that results in the reduction of SHP by quinol and formation of the oxygen complex, which may function as an oxygenase. The three distinct sensors suggest at least as many separate functional roles for SHP. Two of the sensors are not well characterized, but the third is homologous to the QseC quorum sensor, which is present in a number of pathogens and typically appears to regulate genes involved in virulence.
Meyer
Terry E
TE
Department of Chemistry and Biochemistry, University of Arizona, Tucson, 85721, USA. temeyer@u.arizona.edu
Kyndt
John A
JA
Cusanovich
Michael A
MA
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000145:classification / Q000235:genetics*; D000081062:Heme-Binding Proteins; D006420:Hemeproteins / Q000737:chemistry / Q000145:classification / Q000235:genetics*; D008969:Molecular Sequence Data; D009876:Operon; D010088:Oxidoreductases / Q000737:chemistry / Q000145:classification / Q000235:genetics*; D012242:Rhodobacter sphaeroides / Q000235:genetics*; D016415:Sequence Alignment
D001426:Bacterial Proteins; D000081062:Heme-Binding Proteins; D006420:Hemeproteins; C404449:heme protein, bacteria; D010088:Oxidoreductases; C090099:diheme cytochrome c