Photodissociation of heme distal methionine in ferrous cytochrome C revealed by subpicosecond time-resolved resonance Raman spectroscopy.
Cytochrome c (cyt c) is an electron-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 approximately 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.
Cianetti
Simona
S
Laboratory for Optics and Biosciences, INSERM U451, CNRS UMR 7645, Ecole Polytechnique, 91128 Palaiseau Cedex, France.
Négrerie
Michel
M
Vos
Marten H
MH
Martin
Jean-Louis
JL
Kruglik
Sergei G
SG
D045304:Cytochromes c / Q000737:chemistry* / Q000378:metabolism; D006418:Heme / Q000737:chemistry* / Q000378:metabolism; D007700:Kinetics; D008715:Methionine / Q000737:chemistry* / Q000378:metabolism; D010777:Photochemistry; D013059:Spectrum Analysis, Raman / Q000379:methods*
D006418:Heme; D045304:Cytochromes c; D008715:Methionine