title: Ligand binding and protein dynamics in neuroglobin.
abstract: Neuroglobin (Ngb) is a recently discovered protein in vertebrate brain tissue that belongs to the globin family of proteins. It has been implicated in the neuronal response to hypoxia or ischemia, although its physiological role has been hitherto unknown. Ngb is hexacoordinate in the ferrous deoxy form under physiological conditions. To bind exogenous ligands like O(2) and CO, the His E7 endogenous ligand is displaced from the sixth coordination. By using infrared spectroscopy and nanosecond time-resolved visible spectroscopy, we have investigated the ligand-binding reaction over a wide temperature range (3-353 K). Multiple, intrinsically heterogeneous distal heme pocket conformations exist in NgbCO. Photolysis at cryogenic temperatures creates a five-coordinate deoxy species with very low geminate-rebinding barriers. The photodissociated CO is observed to migrate within the distal heme pocket even at 20 K. Flash photolysis near physiological temperature (275-353 K) exhibits four sequential kinetic features: (i) geminate rebinding (t < 1 micros); (ii) extremely fast bimolecular exogenous ligand binding (10 micros < t < 1 ms) with a nontrivial temperature dependence; (iii) endogenous ligand binding (100 micros < t < 10 ms), which can be studied by using flash photolysis on deoxy Ngb; and (iv) displacement of the endogenous by the exogenous ligand (10 ms < t < 10 ks). All four processes are markedly nonexponential, suggesting that Ngb fluctuates among different conformations on surprisingly long time scales.
authors.affiliation: Department of Biophysics, University of Ulm, D-89069 Ulm, Germany.
authors.forename: Jan M
authors.initials: JM
authors.lastname: Kriegl
authors.forename: Aninda J
authors.initials: AJ
authors.lastname: Bhattacharyya
authors.forename: Karin
authors.initials: K
authors.lastname: Nienhaus
authors.forename: Pengchi
authors.initials: P
authors.lastname: Deng
authors.forename: Oleksandr
authors.initials: O
authors.lastname: Minkow
authors.forename: G Ulrich
authors.initials: GU
authors.lastname: Nienhaus
mesh_terms: D000818:Animals; D002245:Carbon Dioxide / Q000378:metabolism; D003001:Cloning, Molecular; D004926:Escherichia coli; D005914:Globins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006418:Heme / Q000378:metabolism; D007700:Kinetics; D008024:Ligands; D051379:Mice; D009419:Nerve Tissue Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D000078787:Neuroglobin; D010100:Oxygen / Q000378:metabolism; D010782:Photolysis; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D013816:Thermodynamics
chemical_list: D008024:Ligands; D009419:Nerve Tissue Proteins; D000078787:Neuroglobin; D011994:Recombinant Proteins; D002245:Carbon Dioxide; D006418:Heme; D005914:Globins; D010100:Oxygen