Novel FixL homologues in Chlamydomonas reinhardtii bind heme and O(2).
Genome inspection revealed nine putative heme-binding, FixL-homologous proteins in Chlamydomonas reinhardtii. The heme-binding domains from two of these proteins, FXL1 and FXL5 were cloned, expressed in Escherichia coli, purified and characterized. The recombinant FXL1 and FXL5 domains stained positively for heme, while mutations in the putative ligand-binding histidine FXL1-H200S and FXL5-H200S resulted in loss of heme binding. The FXL1 and FXL5 [Fe(II), bound O(2)] had Soret absorption maxima around 415 nm, and weaker absorptions at longer wavelengths, in concurrence with the literature. Ligand-binding measurements showed that FXL1 and FXL5 bind O(2) with moderate affinity, 135 and 222 μM, respectively. This suggests that Chlamydomonas may use the FXL proteins in O(2)-sensing mechanisms analogous to that reported in nitrogen-fixing bacteria to regulate gene expression.
Biosciences Center, National Renewable Energy Laboratory, Golden, CO 80401, USA.
U M Narayana
UM
Murthy
Matt S A
MS
Wecker
Matthew C
MC
Posewitz
Marie-Alda
MA
Gilles-Gonzalez
Maria L
ML
Ghirardi
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D016825:Chlamydomonas reinhardtii / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000378:metabolism; D016680:Genome, Bacterial; D006418:Heme / Q000378:metabolism*; D006420:Hemeproteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006639:Histidine / Q000737:chemistry; D000071677:Histidine Kinase; D008969:Molecular Sequence Data; D009154:Mutation; D010100:Oxygen / Q000378:metabolism*; D010766:Phosphorylation; D013053:Spectrophotometry
D001426:Bacterial Proteins; D006420:Hemeproteins; D006418:Heme; D006639:Histidine; C067929:FixL protein, Bacteria; D000071677:Histidine Kinase; D010100:Oxygen