Characterization of two cytochrome b6 proteins from the cyanobacterium Gloeobacter violaceus PCC 7421.
In the genome of the untypical cyanobacterium Gloeobacter violaceus PCC 7421 two potential cytochrome b (6) proteins PetB1 and PetB2 are encoded. Such a situation has not been observed in cyanobacteria, algae and higher plants before, and both proteins are not characterized at all yet. Here, we show that both apo-proteins bind heme with high affinity and the spectroscopic characteristics of both holo-proteins are distinctive for cytochrome b (6) proteins. However, while in PetB2 one histidine residue, which corresponds to H100 and serves as an axial ligand for heme b (H) in PetB1, is mutated, both PetB proteins bind two heme molecules with different midpoint potentials. To recreate the canonical heme b (H) binding cavity in PetB2 we introduced a histidine residue at the position corresponding to H100 in PetB1 and subsequently characterized the generated protein variant. The presented data indicate that two bona fide cytochrome b (6) proteins are encoded in Gloeobacter violaceus. Furthermore, the two petB genes of Gloeobacter violaceus are each organized in an operon together with a petD gene. Potential causes and consequences of the petB and petD gene heterogeneity are discussed.
Institut für Biochemie und Molekularbiologie, ZBMZ, Albert-Ludwigs-Universität Freiburg, 79104, Freiburg, Germany.
Carolin
C
Dreher
Ruth
R
Hielscher
Alexander
A
Prodöhl
Petra
P
Hellwig
Dirk
D
Schneider
D000595:Amino Acid Sequence; D000458:Cyanobacteria / Q000201:enzymology*; D045346:Cytochrome b6f Complex / Q000235:genetics / Q000378:metabolism; D045347:Cytochromes b6 / Q000235:genetics* / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D006418:Heme / Q000378:metabolism; D008969:Molecular Sequence Data; D016296:Mutagenesis; D009876:Operon / Q000235:genetics; D016415:Sequence Alignment
D045347:Cytochromes b6; C084072:petD protein, cytochrome b(6)f complex; D006418:Heme; D045346:Cytochrome b6f Complex