Mitochondrial Metabolism & Biogenesis Lecture PDF

Interactions between mitochondria and the surrounding cell Metabolic Protein import Genetic (next lecture)  CAC Intermediates Are Amphibolic Support degradative and biosynthetic metabolism Red arrows – anaplerotic rxns gluconeogenes...

Interactions between mitochondria and the surrounding cell Metabolic Protein import Genetic (next lecture)  CAC Intermediates Are Amphibolic Support degradative and biosynthetic metabolism Red arrows – anaplerotic rxns gluconeogenesis  Anaplerotic Reactions Intermediates in CAC used in biosynthetic pathways. Must be replenished for the cycle to continue 4-carbon intermediates - formed by carboxylation of 3-carbon precursors. Transfer of metabolites and reducing power in/out of mitochondria – impermeable to NADH Via shuttles (transamination) and metabolite transporters Shuttles: indirect transfer of NADH without membrane bound carrier  Malate-aspartate shuttle (1) Aspartate Aminotransferase (AAT) Intermembrane space Malate- Aspartate- ketoglutarate glutamate transporter transporter Aspartate Aminotransferase (AAT) Transfers reducing power (NADH) from outside to inside mitochondria Liver, Kidney, Heart (or vice-versa) Glycerol-3-Phosphate Shuttle Skeletal muscle, brain G3PDH bound to outer face of IMM. NO membrane transport systems involved. IMM transporters Mitochondrial proteins 25,000 + genes  Mitochondrial assembly Most mitochondrial proteins are nuclear encoded Synthesised on cytoplasmic ribosomes post-translational targeting Four mitochondrial locations: Outer membrane Inner membrane Intermembrane space Matrix space  Mitochondrial protein import Post-translational processing Transit Mature peptide sequence N-terminal amino acid targeting N C sequence (amphipathic helix: +ve and uncharged residues on different sides) = “postal address” Outer and inner mitochondrial membranes contain receptor proteins – bind mitochondrial targeting signal Mitochondrion  In vitro import of nuclear-encoded fumarase & DHFR into yeast mitochondria Protease Fumarase p = precursor m = mature protein DHFR 35S-methionine, rabbit reticulocyte lysate - in vitro transcription, translation of cDNA Mitochondrial Protein Import Mechanisms – everything starts with TOM Tom: Translocase of Outer Membrane But TOM will only get you so far …..needs friends to help find right way home TOM’s friends TIM = Translocon of Inner Membrane PAM = Presequence tranlocase-Associated Motor SAM = Sorting and Assembly Machinery OXA = Oxidase Assembly translocase MIA = Mitochondrial Import and Assembly system Targetting β- Barrel Proteins to Outer Mitochondrial Membrane - TOM meets SAM TOM = Translocon of Outer Membrane TIM = Tim , soluble chaperones in IMS SAM = Sorting and Assembly Machinery Targeting metabolite carriers to Inner Mitochondrial Membrane - Tom meets Tim TOM = Translocon of Outer Membrane TIM (22) = Translocon of Inner Membrane Soluble IMS and mitochondrial matrix protein import - Tom needs Mia and Tim’s older brother MIA = Mitochondrial Import and Assembly system TIM 23 = Translocon of Inner Membrane  Mitochondrial Import of Nuclear Encoded Proteins Mito. Import & Assembly Mitochondrial Processing Peptidase Matrix Protein has targeting sequence removed  Mitochondria Contain a Separate Chromosome Mitochondrial DNA is circular and well conserved. The mitochondrial genome has 37 genes including proteins of mitochondrial encoded oxidative nuclear encoded phosphorylation. Oxa helps nuclear encoded IMM protein meet their mitochondrial genome partner OXA = Oxidase Assembly translocase