title: Increased dynamics in the 40-57 Ω-loop of the G41S variant of human cytochrome c promote its pro-apoptotic conformation.
abstract: Thrombocytopenia 4 is an inherited autosomal dominant thrombocytopenia, which occurs due to mutations in the human gene for cytochrome c that results in enhanced mitochondrial apoptotic activity. The Gly41Ser mutation was the first to be reported. Here we report stopped-flow kinetic studies of azide binding to human ferricytochrome c and its Gly41Ser variant, together with backbone amide H/D exchange and (15)N-relaxation dynamics using NMR spectroscopy, to show that alternative conformations are kinetically and thermodynamically more readily accessible for the Gly41Ser variant than for the wild-type protein. Our work reveals a direct conformational link between the 40-57 Ω-loop in which residue 41 resides and the dynamical properties of the axial ligand to the heme iron, Met80, such that the replacement of glycine by serine promotes the dissociation of the Met80 ligand, thereby increasing the population of a peroxidase active state, which is a key non-native conformational state in apoptosis.
authors.affiliation: School of Biological Sciences, University of Essex, Wivenhoe Park, Colchester, CO4 3SQ, UK.
authors.forename: Andreas Ioannis
authors.initials: AI
authors.lastname: Karsisiotis
authors.affiliation: School of Biological Sciences, University of Essex, Wivenhoe Park, Colchester, CO4 3SQ, UK.
authors.forename: Oliver M
authors.initials: OM
authors.lastname: Deacon
authors.affiliation: School of Biological Sciences, University of Essex, Wivenhoe Park, Colchester, CO4 3SQ, UK.
authors.forename: Michael T
authors.initials: MT
authors.lastname: Wilson
authors.affiliation: School of Chemistry, University of East Anglia, Norwich Research Park, NR4 7TJ, UK.
authors.forename: Colin
authors.initials: C
authors.lastname: Macdonald
authors.affiliation: School of Chemistry, University of East Anglia, Norwich Research Park, NR4 7TJ, UK.
authors.forename: Tharin M A
authors.initials: TM
authors.lastname: Blumenschein
authors.affiliation: School of Chemistry, University of East Anglia, Norwich Research Park, NR4 7TJ, UK.
authors.forename: Geoffrey R
authors.initials: GR
authors.lastname: Moore
authors.affiliation: School of Biological Sciences, University of Essex, Wivenhoe Park, Colchester, CO4 3SQ, UK.
authors.forename: Jonathan A R
authors.initials: JA
authors.lastname: Worrall
mesh_terms: D000577:Amides / Q000737:chemistry; D017209:Apoptosis; D045304:Cytochromes c / Q000737:chemistry* / Q000235:genetics*; D006418:Heme / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D009154:Mutation / Q000235:genetics*; D017433:Protein Structure, Secondary; D013816:Thermodynamics
chemical_list: D000577:Amides; D006418:Heme; D045304:Cytochromes c