Comparison of the structural dynamic and mitochondrial electron-transfer properties of the proapoptotic human cytochrome c variants, G41S, Y48H and A51V.

Mitochondrial cytochrome c is associated with electron transfer in the respiratory chain and in apoptosis. Four cytochrome c variants have been identified in families that suffer from mild autosomal dominant thrombocytopenia, a platelet disorder associated with increased apoptosis. Three out of the four substitutions, G41S, Y48H and A51V are located on the 40-57 Ω-loop.

Naturally Occurring Disease-Related Mutations in the 40-57 Ω-Loop of Human Cytochrome c Control Triggering of the Alkaline Isomerization.

Naturally occurring mutations found in one of the two Ω-loop substructures in human cytochrome c are associated with low blood platelet count (thrombocytopenia). Both Ω-loops participate in the formation of conformers associated with cytochrome c peroxidase activity and apoptotic function. At alkaline pH values, the Met80 ligand to the ferric heme iron dissociates, and a lysine residue in the 71-85 Ω-loop coordinates to the iron.

Heightened Dynamics of the Oxidized Y48H Variant of Human Cytochrome c Increases Its Peroxidatic Activity.

Proteins performing multiple biochemical functions are called "moonlighting proteins" or extreme multifunctional (EMF) proteins. Mitochondrial cytochrome c is an EMF protein that binds multiple partner proteins to act as a signaling molecule, transfers electrons in the respiratory chain, and acts as a peroxidase in apoptosis. Mutations in the cytochrome c gene lead to the disease thrombocytopenia, which is accompanied by enhanced apoptotic activity.

Near-complete backbone resonance assignments of acid-denatured human cytochrome c in dimethylsulfoxide: a prelude to studying interactions with phospholipids.

Human cytochrome c plays a central role in the mitochondrial electron transfer chain and in the intrinsic apoptosis pathway. Through the interaction with the phospholipid cardiolipin, cytochrome c triggers release of pro-apoptotic factors, including itself, from the mitochondrion into the cytosol of cells undergoing apoptosis. The cytochrome c/cardiolipin complex has been extensively studied through various spectroscopies, most recently with high-field solution and solid-state NMR spectroscopies, but there is no agreement between the various studies on key structural features of cytochrome c in its complex with cardiolipin.

Increased dynamics in the 40-57 Ω-loop of the G41S variant of human cytochrome c promote its pro-apoptotic conformation.

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.