Redox-mediated transcriptional activation in a CooA variant.
CooA, the carbon monoxide-sensing transcription factor from Rhodospirillum rubrum, binds CO at a reduced (Fe(II)) heme moiety with resulting conformational changes that promote DNA binding. In this study, we report a variant of CooA, M124R, that is active in transcriptional activation in a redox-dependent manner. Where wild-type CooA is active only in the Fe(II) + CO form, M124R CooA is active in both Fe(II) + CO and Fe(III) forms. Analysis of the pH dependence of the activity of Fe(III) M124R CooA demonstrated that the activity was also coordination state-dependent with a five-coordinate, high-spin species identified as the active form and Cys(75) as the retained ligand. In contrast, the active Fe(II) + CO forms of both wild-type and M124R CooA are six-coordinate and low-spin with a protein ligand other than Cys(75), so that WT and Fe(III) M124R CooA are apparently achieving an active conformation despite two different heme coordination and ligation states. A hypothesis to explain these results is proposed. This study demonstrates the utility of CooA as a model system for the isolation of functionally interesting heme proteins.
Thorsteinsson
M V
MV
Departments of Bacteriology and Biochemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
Kerby
R L
RL
Youn
H
H
Conrad
M
M
Serate
J
J
Staples
C R
CR
Roberts
G P
GP
D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics*; D029968:Escherichia coli Proteins; D036781:Fimbriae Proteins; D008958:Models, Molecular; D010084:Oxidation-Reduction; D011487:Protein Conformation; D012247:Rhodospirillum rubrum / Q000378:metabolism*; D015533:Transcriptional Activation; D001616:beta-Galactosidase / Q000235:genetics
D001426:Bacterial Proteins; C088904:CooA protein, E coli; D029968:Escherichia coli Proteins; D036781:Fimbriae Proteins; D001616:beta-Galactosidase