Photodissociation of heme distal methionine in ferrous cytochrome c revealed by subpicosecond time-resolved resonance raman spectroscopy

Abstract : Cytochrome c (cyt c) is anelectron-transfer heme protein that also binds nitric oxide (NO). In resting cyt c, two endogenous ligands of the heme iron are histidine-18 (His) and methionine-80 (Met) side chains, and NO binding requires the cleavage of one of the axial bonds. Previous femtosecond transient absorption studies suggested the photolysis of either Fe-His or Fe-Met bonds. We aimed at unequivocally identifying the internal side chain that is photodissociated in ferrous cyt c and at monitoring heme structural dynamics, by means of time-resolved resonance Raman (TR3) spectroscopy with ~0.6 ps time resolution. The Fe-His stretching mode at 216 cm-1 has been observed in photoproduct TR3 spectra for the first time for a c-type heme. The same transient mode was observed for a model ferrous cyt c N-fragment (residues 1-56) ligated with two His in the resting state. Our TR3 data reveal that upon ferrous cyt c photoexcitation, (i) distal Met side chain is instantly released, producing a five-coordinated domed heme structure, (ii) proximal His side chain, coupled to the heme, exhibits distortion due to strain exerted by the protein, and (iii) alteration in heme-cysteine coupling takes place along with the relaxation of the protein-induced deformations of the heme macrocycle. Copyright 2004 American Chemical Society.
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Simona Cianetti, Michel Négrerie, Marten Vos, Jean-Louis Martin, Sergei Kruglik. Photodissociation of heme distal methionine in ferrous cytochrome c revealed by subpicosecond time-resolved resonance raman spectroscopy. Journal of the American Chemical Society, American Chemical Society, 2004, 126 (43), pp.13932. ⟨10.1021/ja046442i⟩. ⟨hal-00836427⟩

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