Burstyn Group
Bioinorganic Chemistry at the University of Wisconsin
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CooA
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CooA is a CO-sensing
transcriptional activator found in the lake-dwelling bacterium Rhodospirillum rubrum.
The binding of CooA to its target DNA sequence results in transcription of genes
that encode a CO-oxidation system, allowing R. rubrum to live on CO as its sole energy
source. Like many gas-sensing proteins, CooA contains a heme cofactor, which serves as
a recognition site for CO.
Although CooA is the only known CO sensor, evidence suggests that CO may also be
an important signaling molecule in higher organisms. In collaboration with the
laboratory of
Professor Gary Roberts (UW Bacteriology), we are
investigating the chemistry that occurs at heme in CooA to elucidate the role of
this cofactor in the CO-dependent activation mechanism. Binding of CO to the
ferrous heme in CooA results in the displacement of an endogenous heme ligand.
Crystallographic studies of Fe(II) CooA demonstrated that the heme is remote
from the DNA-binding domain, implying that the signal propagation occurs via an
allosteric mechanism. To determine the critical factors responsible for signal
transmission in CooA, we utilize techniques such as electronic absorption, EPR,
MCD, and fluorescence spectroscopies, along with electrochemical
characterization. Correlating CooA structural changes resulting from CO binding
with the activation of DNA binding may provide a clearer understanding of
allostery in gas-sensing heme proteins.
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| CO binding to the CooA heme appears to cause a dramatic repositioning of the DNA-binding domain (right). The proposed "active" structure of CooA was created by combining the crystal structures of inactive Fe(II) CooA and a homologous DNA-binding protein in the active state. We are currently investigating this model of the CooA conformational states by methods including chemical denaturation and protein fluorescence. |
