The solution structure of polypeptides can now be achieved through NMR spectroscopy, as long as the molecular mass does not much exceed 40 000 Da [1][2][3][4][5]. The determination of the structure of heme proteins, however, requires the knowledge of the position of the iron and of the atoms of the heme with respect to the protein frame. While the latter can be achieved, as far as the protons are concerned, from NOEs data, the former is difficult to achieve.
As heme proteins in some of their active forms contain the iron ion in a paramagnetic state, a strategy which exploits the contributions to the relaxation rates and the pseudocontact shifts originating from the paramagnetic metal ion has been developed [6][7][8][9][10][11][12] and the constraints derived from these contributions have been successfully used in structure determination [6,7,12]. Furthermore, these constraints are the only ones which allow the location of the iron ion within the protein frame, without any assumption. However, the overall geometry of the heme and its deviation from planarity are essentially based on the X-ray determination and on molecular dynamics calculations. These various problems in the structure determination will be extensively discussed at the symposium.
Whatever the way of introducing the heme into the protein frame, several structures have now been solved .
NMR studies of heme proteins also provided clear insights on the backbone NH exchangeability, on the NH or CH conformational exchange processes, as long as they occur within a 10 Γ3 -10 Γ6 s timescale, and on the subnanosecond timescale motions [45][46][47][48][49][50][51][52][53][54][55][56].
Finally, protein-protein interactions will also be treated. This is an important aspect, as many heme proteins are electron transfer proteins and the latter are involved in electron transfer pathways where they interact with other proteins [63,64].
Molecular dynamics simulations can be invaluable, as they can be used to refine the structure, to monitor the protein mobility and to understand the factors which determine the different structural and dynamical properties in the different oxidation states [57][58][59][60][61][62].
In perspective, these studies will give a rationale for the differences induced by the oxidation states and by the protein-protein interactions.