Biophysical properties of a c-type heme in chemotaxis signal transducer protein DcrA.
Chemotaxis signal transducer protein DcrA from a sulfate-reducing bacterium Desulfovibrio vulgaris Hildenborough was previously shown to contain a c-type heme in its periplasmic domain (DcrA-N) for sensing redox and/or oxygen [Fu et al. (1994) J. Bacteriol. 176, 344-350], which is the first example of a heme-based sensor protein containing a c-type heme as a prosthetic group. Optical absorption and resonance Raman spectroscopies indicates that heme c in DcrA-N shows a redox-dependent ligand exchange. Upon reduction, a water molecule that may be the sixth ligand of the ferric heme c is replaced by an endogenous amino acid. Although the reduced heme in DcrA-N is six-coordinated with two endogenous axial ligands, CO can easily bind to the reduced heme to form CO-bound DcrA-N. Reaction of the reduced DcrA-N with molecular oxygen results in autoxidation to form a ferric state without forming any stable oxygen-bound form probably due to the extremely low redox potential of DcrA-N (-250 mV). Our study supports the initial idea by Fu et al. that DcrA would act as a redox and/or oxygen sensor, in which the ligand exchange between water and an endogenous amino acid is a trigger for signal transduction. While the affinity of CO to DcrA-N (Kd = 138 microM) is significantly weak compared to those of other heme proteins, we suggest that CO might be another physiological effector molecule.
Yoshioka
Shiro
S
Okazaki Institute for Integrative Bioscience, National Institutes of Natural Sciences, 5-1, Higashiyama, Myodaiji, Okazaki 444-8787, Japan.
Kobayashi
Katsuaki
K
Yoshimura
Hideaki
H
Uchida
Takeshi
T
Kitagawa
Teizo
T
Aono
Shigetoshi
S
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry*; D055592:Biophysical Phenomena; D001703:Biophysics; D002248:Carbon Monoxide / Q000737:chemistry; D002633:Chemotaxis; D004563:Electrochemistry; D006418:Heme / Q000031:analogs & derivatives* / Q000737:chemistry; D008565:Membrane Proteins / Q000737:chemistry*; D010084:Oxidation-Reduction; D017434:Protein Structure, Tertiary; D015398:Signal Transduction; D013053:Spectrophotometry; D013059:Spectrum Analysis, Raman
D001426:Bacterial Proteins; D008565:Membrane Proteins; C085429:dcrA protein, Desulfovibrio vulgaris; C031690:heme C; D006418:Heme; D002248:Carbon Monoxide