Structural dynamics of proximal heme pocket in HemAT-Bs associated with oxygen dissociation

HemAT from Bacillus subtilis (HemAT-Bs) is a heme-containing O2 sensor protein that acts as a chemotactic signal transducer. Binding of O2 to the heme in the sensor domain of HemAT-Bs induces a conformational change in the protein matrix, and this is transmitted to a signaling domain. To characterize the specific mechanism of O2-dependent conformational changes in HemAT-Bs, we investigated time-resolved resonance Raman spectra of the truncated sensor domain and the full-length HemAT-Bs upon O2 and CO dissociation. A comparison between the O2 and CO complexes provides insights on O2/CO discrimination in HemAT-Bs. While no spectral changes upon CO dissociation were observed in our experimental time window between 10 ns and 100 μs, the band position of the stretching mode between the heme iron and the proximal histidine, ν(Fe–His), for the O2-dissociated HemAT-Bs was lower than that for the deoxy form on time-resolved resonance Raman spectra. This spectral change specific to O2 dissociation would be associated with the O2/CO discrimination in HemAT-Bs. We also compared the results obtained for the truncated sensor domain and the full-length HemAT-Bs, which showed that the structural dynamics related to O2 dissociation for the full-length HemAT-Bs are faster than those for the sensor domain HemAT-Bs. This indicates that the heme proximal structural dynamics upon O2 dissociation are coupled with signal transduction in HemAT-Bs.

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► Ligand-dependent changes were observed in time-resolved resonance Raman spectra.
► The signaling domain was found to affect the structural change in the heme pocket.
► A coupling mechanism between the heme pocket and the signaling domain was proposed.