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Kinetic properties and protein conformational dynamics of the signal transducer HemAT as revealed by time‐resolved stepscan FTIR spectroscopy

HemAT is a heme‐based O2 sensor protein that acts as a signal transducer for aerotaxis in Bacillus subtilis. In our work, we have employed time‐resolved step‐scan Fourier transform infrared (TRS2‐FTIR) spectroscopy to investigate the protein structural changes induced by ligand (CO) photodissociation and rebinding that are crucial for understanding the initial events of the intramolecular signal transduction mechanism in HemAT. We have studied the full length and truncated sensor domain HemAT‐CO adducts as well as the Y70F, L92A, T95A and Y133F mutants. Monitoring the rebinding of CO to the heme‐Fe2+ reveals biphasic kinetics for both the full length and truncated sensor domain HemAT. The TRS2‐FTIR experiments demonstrate that Y70 affects the conformational changes that are induced to the protein matrix by CO photodissociation. Moreover, L92 appears to operate as the conformational gate in the migration pathway of photodissociated CO.