Structural and allosteric transitions of heme protein sensors probed from picosecond to second

The human receptor of nitric oxide (NO), named soluble guanylate cyclase (sGC), is a heme protein present in numerous cells and possesses two functional remote domains: the sensing domain which harbours the heme cofactor and the catalytic domain which synthesizes cGMP from GTP. The synthesis of the cellular messenger cGMP in the catalytic domain is triggered upon NO binding to the heme thanks to a structural allosteric change. Structural transitions are induced at the heme level by NO binding to and release from sGC. I will present how time-resolved absorption spectroscopy in the UV-visible range in the broad time range from 1 picosecond to 1 second allowed to probe localized structural events. Structural allosteric transitions of the NO-receptor, correlated with NO dynamics, were also detected. Time-resolved absorption spectroscopy was also used to decipher the mechanism of action of sGC activators which are artificial drugs and act in the absence of NO. The dynamics of heme-bound side-chains, like methionine as the 6^th iron ligand in mitochondrial cytochrome c, could be measured and revealed a conformational change in the protein.