Identification of histidine 77 as the axial heme ligand of carbonmonoxy CooA by picosecond time-resolved resonance Raman spectroscopy.
The heme proximal ligand of carbonmonoxy CooA, a CO-sensing transcriptional activator, in the CO-bound form was identified to be His77 by using picosecond time-resolved resonance Raman spectroscopy. On the basis of the inverse correlation between Fe-CO and C-O stretching frequencies, we proposed previously that His77 is the axial ligand trans to CO [Uchida et al. (1998) J. Biol. Chem. 273, 19988-19992], whereas later a possibility of displacement of His77 by CO with retention of another unidentified axial ligand was reported [Vogel et al. (1999) Biochemistry 38, 2679-2687]. Although our previous resonance Raman study failed to detect the Fe-His stretching [nu(Fe-His)] mode of CO-photodissociated CooA of the carbonmonoxy adduct due to the rapid recombination, application of the picosecond time-resolved resonance Raman technique enabled us to observe a new intense line assignable to nu(Fe-His) at 211 cm(-)(1) immediately after photolysis, while it became nondiscernible after 100-ps delay. The low nu(Fe-His) frequency of photodissociated CooA indicates the presence of some strain in the Fe-His bond in CO-bound CooA. This and the rapid recombination of CO characterize the heme pocket of CooA. The 211 cm(-)(1) band was completely absent in the spectrum of the CO-photodissociated form of the His77-substituted mutant but the Fe-Im stretching band was observed in the presence of exogenous imidazole (Im). Thus, we conclude that His77 is the axial ligand of CO-bound CooA and CO displaces the axial ligand trans to His77 with retention of ligated His77 to activate CooA as the transcriptional activator.
Uchida
T
T
Institute for Molecular Science, Okazaki National Research Institutes, Myodaiji, Okazaki 444-8585, Japan.
Ishikawa
H
H
Ishimori
K
K
Morishima
I
I
Nakajima
H
H
Aono
S
S
Mizutani
Y
Y
Kitagawa
T
T
D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics; D002248:Carbon Monoxide / Q000737:chemistry*; D004926:Escherichia coli; D029968:Escherichia coli Proteins; D036781:Fimbriae Proteins; D006418:Heme / Q000737:chemistry*; D006639:Histidine / Q000737:chemistry* / Q000235:genetics; D007093:Imidazoles / Q000737:chemistry; D007501:Iron / Q000737:chemistry; D008024:Ligands; D016297:Mutagenesis, Site-Directed; D009211:Myoglobin / Q000031:analogs & derivatives* / Q000737:chemistry; D010782:Photolysis; D013059:Spectrum Analysis, Raman / Q000379:methods; D014443:Tyrosine / Q000235:genetics
D001426:Bacterial Proteins; C088904:CooA protein, E coli; D029968:Escherichia coli Proteins; D007093:Imidazoles; D008024:Ligands; D009211:Myoglobin; C055547:deoxymyoglobin; D036781:Fimbriae Proteins; D014443:Tyrosine; D006418:Heme; D006639:Histidine; C029899:imidazole; D002248:Carbon Monoxide; D007501:Iron