Combining Raman and XRD to study heme proteins

Neuroglobin variants show structural differences associated with perturbation of heme ligand binding. Loop mutants, with enhanced flexibility, have been studied: their ferric resonance Raman spectra in solution and in crystals are almost identical. Two protein conformers with a reversed (A) or a canonical (B) heme insertion orientation have been highlighted. Their abundance could be predicted from Raman marker bands and match X‐ray crystallography results. For the first time a reversed heme insertion has been identified by resonance Raman in a native 6‐coordinate low spin heme protein. This diagnostic tool could be extended to other heme proteins in order to detect ligand orientational disorder, which are likely to be correlated to functionally relevant heme dynamics.