Research highlight: coordination and redox state-dependent structural changes of the heme-based oxygen sensor AfGcHK associated with intraprotein signal transduction
Structural changes in crystal structure of of AfGcHK sensor protein induced by sodium dithionite soaking (PDB ID 5OHF) and conformational changes revealed by HDX-MS. (A) Two protein chains of the heme domain of the sensor protein observed in crystal structure including alternative B (yellow) occurring with dithionite soaking. (B) Conformational changes revealed by HDX-MS after 60 min of deuteration of the full-length AfGcHK proteins visualized on the protein structure. Differences between the Fe(III)-OH- form (active) and inactive Fe(II) form are color coded: grey - no difference, red - higher and blue - lower levels of deuteration.
The heme-based oxygen sensor histidine kinase AfGcHK is part of a two-component signal transduction system in bacteria. O2 binding to the Fe(II) heme complex of its N-terminal globin domain strongly stimulates autophosphorylation at His-183 in its C-terminal kinase domain. The 6-coordinate heme Fe(III)-OH- and -CN- complexes of AfGcHK are also active, but the 5-coordinate heme Fe(II) complex and the heme-free apo-form are inactive. The crystal structures of the isolated dimeric globin domains of the active Fe(III)-CN- and inactive 5-coordinate Fe(II) forms were determined, revealing striking structural differences on the heme-proximal side of the globin domain. Using hydrogen/deuterium exchange coupled with mass spectrometry (HDX–MS) the intramolecular signal transduction mechanisms was investigated in full length AfGcHK. The results suggest that structural changes at the heme proximal side, the globin domain-dimerization interface, and the ATP-binding site are important in the signal transduction mechanism of AfGcHK. For the first time, the conformational changes associated with signal transduction were studied in a full-length globin-coupled oxygen sensor protein and linked to directly observed structural changes in the globin domain.
Stranava, M.; Man, P; Skálová, T.; Kolenko, P; Blaha, J.; Fojtikova, V .; Martínek, V.; Dohnálek, J.; Lengalova, A.; Rosůlek, M.; Shimizu, T.; Martínková, M.: Coordination and redox state-dependent structural changes of the heme-based oxygen sensor AfGcHK associated with intraprotein signal transduction. J. Biol. Chem. first Published on November 1, 2017, doi: 10.1074/jbc.M117.817023jbc.M117.817023.