Charge-state-distribution analysis of Bach2 intrinsically disordered heme binding region.

Bach2 is a transcriptional repressor that plays an important role in the differentiation of T-cells and B-cells. Bach2 is functionally regulated by heme binding, and possesses five Cys-Pro Cys-Pro (CP)-motifs as the heme binding site. To reveal the molecular mechanism of heme binding by Bach2, the intrinsically disordered heme binding region (a.a. 331-520; Bach2331-520) and its CP-motif mutant were prepared and characterized with and without heme, by UV-Vis spectroscopy and thermal profiles. In addition, the charge-state-distributions (CSDs) were assessed by electrospray ionization mass spectrometry. The UV-Vis spectroscopy revealed a lack of five-coordinated heme binding in the CP-motif mutant of Bach2331-520 The thermal profile and CSDs of Bach2331-520 indicated that heme binding induces the destabilization of Bach2331-520 The thermal profile revealed that the wild type Bach2331-520 was destabilized more than the CP-motif mutant. The shift in the CSDs by heme binding suggested that heme binding causes Bach2331-520 to adopt a more compact conformation. In addition, heme binding to the CP-motif could reduce the flexibility of Bach2331-520 Consequently, the five-coordinated heme binding destabilizes Bach2331-520, by reducing the flexibility of the polypeptide chain.