title: Hyperthermal stability of neuroglobin and cytoglobin.
abstract: Neuroglobin (Ngb) and cytoglobin (Cygb), recent additions to the globin family, display a hexa-coordinated (bis-histidyl) heme in the absence of external ligands. Although these proteins have the classical globin fold they reveal a very high thermal stability with a melting temperature (Tm) of 100 degrees C for Ngb and 95 degrees C for Cygb. Moreover, flash photolysis experiments at high temperatures reveal that Ngb remains functional at 90 degrees C. Human Ngb may have a disulfide bond in the CD loop region; reduction of the disulfide bond increases the affinity of the iron atom for the distal (E7) histidine, and leads to a 3 degrees C increase in the T(m) for ferrous Ngb. A similar Tm is found for a mutant of human Ngb without cysteines. Apparently, the disulfide bond is not involved directly in protein stability, but may influence the stability indirectly because it modifies the affinity of the distal histidine. Mutation of the distal histidine leads to lower thermal stability, similar to that for other globins. Only globins with a high affinity of the distal histidine show the very high thermal stability, indicating that stable hexa-coordination is necessary for the enhanced thermal stability; the CD loop which contains the cysteines appears as a critical region in the neuroglobin thermal stability, because it may influence the affinity of the distal histidine.
authors.affiliation: Inserm U473, Le Kremlin-Bicêtre, France.
authors.forename: Djemel
authors.initials: D
authors.lastname: Hamdane
authors.forename: Laurent
authors.initials: L
authors.lastname: Kiger
authors.forename: Sylvia
authors.initials: S
authors.lastname: Dewilde
authors.forename: Julien
authors.initials: J
authors.lastname: Uzan
authors.forename: Thorsten
authors.initials: T
authors.lastname: Burmester
authors.forename: Thomas
authors.initials: T
authors.lastname: Hankeln
authors.forename: Luc
authors.initials: L
authors.lastname: Moens
authors.forename: Michael C
authors.initials: MC
authors.lastname: Marden
mesh_terms: D000818:Animals; D002942:Circular Dichroism; D003486:Cyanides / Q000378:metabolism / Q000494:pharmacology; D003545:Cysteine / Q000235:genetics / Q000378:metabolism; D000078842:Cytoglobin; D004220:Disulfides / Q000737:chemistry / Q000378:metabolism; D004331:Drosophila melanogaster; D005914:Globins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D006639:Histidine / Q000235:genetics / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D008024:Ligands; D008958:Models, Molecular; D009419:Nerve Tissue Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D000078787:Neuroglobin; D011489:Protein Denaturation; D013696:Temperature; D013816:Thermodynamics
chemical_list: C000627265:CYGB protein, human; D003486:Cyanides; D000078842:Cytoglobin; D004220:Disulfides; D008024:Ligands; D009419:Nerve Tissue Proteins; D000078787:Neuroglobin; D006639:Histidine; D005914:Globins; D003545:Cysteine