title: Conformational change and human cytochrome c function: mutation of residue 41 modulates caspase activation and destabilizes Met-80 coordination.
abstract: Cytochrome c is a highly conserved protein, with 20 residues identical in all eukaryotic cytochromes c. Gly-41 is one of these invariant residues, and is the position of the only reported naturally occurring mutation in cytochrome c (human G41S). The basis, if any, for the conservation of Gly-41 is unknown. The mutation of Gly-41 to Ser enhances the apoptotic activity of cytochrome c without altering its role in mitochondrial electron transport. Here we have studied additional residue 41 variants and determined their effects on cytochrome c functions and conformation. A G41T mutation decreased the ability of cytochrome c to induce caspase activation and decreased the redox potential, whereas a G41A mutation had no impact on caspase induction but the redox potential increased. All residue 41 variants decreased the pK                 (a) of a structural transition of oxidized cytochrome c to the alkaline conformation, and this correlated with a destabilization of the interaction of Met-80 with the heme iron(III) at physiological pH. In reduced cytochrome c the G41T and G41S mutations had distinct effects on a network of hydrogen bonds involving Met-80, and in G41T the conformational mobility of two Ω-loops was altered. These results suggest the impact of residue 41 on the conformation of cytochrome c influences its ability to act in both of its physiological roles, electron transport and caspase activation.
authors: Department of Biochemistry, University of Otago, PO Box 56, Dunedin, 9054, New Zealand.
authors: Tracy M
authors: TM
authors: Josephs
authors: Matthew D
authors: MD
authors: Liptak
authors: Gillian
authors: G
authors: Hughes
authors: Alexandra
authors: A
authors: Lo
authors: Rebecca M
authors: RM
authors: Smith
authors: Sigurd M
authors: SM
authors: Wilbanks
authors: Kara L
authors: KL
authors: Bren
authors: Elizabeth C
authors: EC
authors: Ledgerwood
mesh_terms: D019943:Amino Acid Substitution; D017209:Apoptosis; D020169:Caspases / Q000378:metabolism*; D045744:Cell Line, Tumor; D045304:Cytochromes c / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D004789:Enzyme Activation; D005998:Glycine / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D006801:Humans; D007501:Iron / Q000378:metabolism; D008715:Methionine / Q000737:chemistry / Q000378:metabolism*; D008958:Models, Molecular; D019906:Nuclear Magnetic Resonance, Biomolecular; D010084:Oxidation-Reduction; D017354:Point Mutation; D011487:Protein Conformation
chemical_list: D045304:Cytochromes c; D008715:Methionine; D007501:Iron; D020169:Caspases; D005998:Glycine