title: Ultrafast heme-residue bond formation in six-coordinate heme proteins: implications for functional ligand exchange.
abstract: A survey is presented of picosecond kinetics of heme-residue bond formation after photolysis of histidine, methionine, or cysteine, in a broad range of ferrous six-coordinate heme proteins. These include human neuroglobin, a bacterial heme-binding superoxide dismutase (SOD), plant cytochrome b 559, the insect nuclear receptor E75, horse heart cytochrome c and the heme domain of the bacterial sensor protein Dos. We demonstrate that the fastest and dominant phase of binding of amino acid residues to domed heme invariably takes place with a time constant in the narrow range of 5-7 ps. Remarkably, this is also the case in the heme-binding SOD, where the heme is solvent-exposed. We reason that this fast phase corresponds to barrierless formation of the heme-residue bond from a configuration close to the bound state. Only in proteins where functional ligand exchange occurs, additional slower rebinding takes place on the time scale of tens of picoseconds after residue dissociation. We propose that the presence of these slower phases reflects flexibility in the heme environment that allows external ligands (O2, CO, NO, . . .) to functionally replace the internal residue after thermal dissociation of the heme-residue bond.
authors.affiliation: Laboratoire d'Optique et Biosciences, CNRS, Ecole Polytechnique, F-91128 Palaiseau, France. marten.vos@polytechnique.edu
authors.forename: Marten H
authors.initials: MH
authors.lastname: Vos
authors.forename: Andrea
authors.initials: A
authors.lastname: Battistoni
authors.forename: Christophe
authors.initials: C
authors.lastname: Lechauve
authors.forename: Michael C
authors.initials: MC
authors.lastname: Marden
authors.forename: Laurent
authors.initials: L
authors.lastname: Kiger
authors.forename: Alain
authors.initials: A
authors.lastname: Desbois
authors.forename: Eric
authors.initials: E
authors.lastname: Pilet
authors.forename: Eve
authors.initials: E
authors.lastname: de Rosny
authors.forename: Ursula
authors.initials: U
authors.lastname: Liebl
mesh_terms: D000818:Animals; D001671:Biochemistry / Q000379:methods; D045304:Cytochromes c / Q000737:chemistry; D004330:Drosophila; D004926:Escherichia coli / Q000378:metabolism; D005914:Globins / Q000737:chemistry; D006191:Haemophilus ducreyi / Q000378:metabolism; D006418:Heme / Q000737:chemistry*; D006420:Hemeproteins / Q000737:chemistry*; D006736:Horses; D006801:Humans; D008024:Ligands; D009419:Nerve Tissue Proteins / Q000737:chemistry; D000078787:Neuroglobin; D010100:Oxygen / Q000737:chemistry; D018724:Spinacia oleracea / Q000378:metabolism; D013482:Superoxide Dismutase / Q000737:chemistry*
chemical_list: D006420:Hemeproteins; D008024:Ligands; D009419:Nerve Tissue Proteins; D000078787:Neuroglobin; D006418:Heme; D005914:Globins; D045304:Cytochromes c; D013482:Superoxide Dismutase; D010100:Oxygen