tailieunhanh - Báo cáo khoa học: Hyperthermal stability of neuroglobin and cytoglobin

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 C for Ngb and 95 C for Cygb. Moreover, flash photolysis experi-ments at high temperatures reveal that Ngb remains functional at 90 C | iFEBS Journal Hyperthermal stability of neuroglobin and cytoglobin Djemel Hamdane1 Laurent Kiger1 Sylvia Dewilde2 Julien Uzan1 Thorsten Burmester3 Thomas Hankeln4 Luc Moens2 and Michael C Marden1 1 Inserm U473 Le Kremlin-Bicetre France 2 Department of BiomedicalSciences University of Antwerp Belgium 3 Institute of Zoology Johannes Gutenberg University of Mainz Germany 4 Institute of Molecular Genetics Johannes Gutenberg University of Mainz Germany Keywords cytoglobin disulfide bond ligand kinetics neuroglobin protein melting temperature Correspondence M. C. Marden Inserm U473 78 rue du GeneralLeclerc 94275 Le Kremlin-Bicetre France E-mail marden@ Received 6 December 2004 revised 14 February 2005 accepted 1 March 2005 doi 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 C for Ngb and 95 C for Cygb. Moreover flash photolysis experiments at high temperatures reveal that Ngb remains functional at 90 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 C increase in the Tm 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 .