The formation of hydrogen bond in the proximal heme pocket of HemAT-Bs upon ligand binding

HemAT-Bs is the heme-based O2 sensor responsible for aerotaxis control in Bacillus subtilis. In this study, we measured the time-resolved resonance Raman spectra of full-length HemAT-Bs wild-type (WT) and Y133F in the deoxy form and the photoproduct after photolysis of CO-bound form. In WT, the νFe-His band for the 10 ps photoproduct was observed at higher frequency by about 2 cm−1 compared with that of the deoxy form. This frequency difference is relaxed in hundreds of picoseconds. This time-dependent frequency shift would reflect the conformational change of the protein matrix. On the other hand, Y133F mutant did not show such a substantial νFe-His frequency shift after photolysis. Since a hydrogen bond to the proximal His induces an up-shift of the νFe-His frequency, these results indicate that Tyr133 forms a hydrogen bond to the proximal His residue upon the ligand binding. We discuss a functional role of this hydrogen bond formation for the signal transduction in HemAT-Bs.