The transport of proteins into mitochondria and chloroplasts
Newly mito & chloropl are produced by the growth of preexisting organelle. Their growth depends mainly on the cytosolic protein import
Translocation into the mitochondrial matrix depends on a signal sequence and protein translocators
Red = + Yellow = nonpolar On different side Amphipathic helix
translocase Require for import all nucleus-encoded mitochondria protein Insert to inner memb. Transport to matrix For protein syn In mito
Mitchondrial precursor proteins are imported as unfolded polypeptide chains Interacting protein: eg Charperone protein hsp70 family All Interacting protein help to prevent aggregation before engaging with TOM complex in outer mito membrane.
Mitochondrial precursor proteins are imported into the matrix at contact sites that join the inner and outer membranes
Protein import by mitochondria
ATP hydrolysis and a H + gradient are used to drive protein import into mitochondria
pulling Freely permeable to ions and metabolites but not to most protein Charperone protein also function as translocator
Repeated cycles of ATP hydrolysis by mitochondrial Hsp70 complete the import process. Hsp 60 provide chamber for unfolded polypeptide chain facilitates folding (chapter 6)
Protein transport into the inner mitochondrial membrane and the intermembrane space required two signal sequences
Two signal sequences are required to direct proteins to the thylakoid membrane in chloroplasts Resemble in mitochondria
Peroxisomes use molecular oxygen and hydrogen peroxide to perform oxidative reactions
Catalase: 2H2O2 2H2O + O2 Urate oxidase: RH2 + O2 R + H2O2 Animal: -oxidation occur at both mitochondria & perixosome. Plant & yeast: -oxidation occur only at perixosome.
Plasmalogen -the most abundant protein in myelin. - deficient result in neurological disease. Animal Perxisome catalyze the first step for plasmalogen biosyn
A short signal sequence directs the import of proteins into peroxisomes
Peroxins: -at least 23 distinct proteins for driving ATP hydrolysis -deficent result in Zellweger syndrome. Most peroxisomal membrane proteins are made in the cytosol insert into preexisting peroxisomes.
The endoplasmic reticulum
Membrane-bound ribosomes define the rough ER
Many ribosomes bind to a single mRNA
ER capture 2 type of protein: transmembrane protein & water-sol protein Cotranslatioal transport? Posttranslational transport?
p690 In mammalian cells Protein import to ER Cotranslational process (chaperone are not required to keep protein unfolded) Protein import to mitochondria, chloroplasts, nuclei, peroxisomes Postranslational process (chaperone needed for unfolding) Compared to page 697
Smooth ER abundant in some specialized cells
Lipid metabolism (cholestersol) Detoxification by cytochrome p450 Sequester Ca+2 from cytosol (SR) Autophagocytosis & phenobarital
Rough and smooth regions of ER can be separated by centrifugation
Signal sequences were first discovered in proteins imported into the rough ER
A signal-recognition particle (SRP) directs ER signal sequences to a specific receptor in the rough ER membrane
ER & SRP for import
The polypeptide chain passes through an aqueous pore in the translocator
Translocation across the ER membrane does not always require ongoing polypeptide chain elongation
yeast ATPase Binding protein (hsp70-like chaperone protein) Protein that are are first released into cytosol (bind to hsp to prevent folding) c/o sealing the pore
The ER sequence is removed from most soluble proteins after translocation
In single-pass transmembrane proteins, a single internal ER signal sequence remains in the lipid bilayer as membrane- spanning of a helix
Combinations of start-transfer and stop-transfer signals determine the topology of multipass transmembrane proteins
Translocated polypeptide chains fold and assemble in the lumen of the rough ER Important ER resident proteins: PDI (protein disulfide isomerase; produce -s-s-) BiP chaperone protein (prevent aggregate & help to keep in ER)
Most (Soluble & membrane- bounded) proteins synthesized in the RER are glycosylated by the addition of a common N-linked oligosaccharide Very few protein in cytosol is glycosylated.
N-linked oligosaccharide - are by far the most common oligosaccharides found in glycoprotein. (RER) -are recognized by 2 ER charperon protein (calnexin & calreticulin) O-linked oligosaccharide are found in Golgi.
Oligosaccharides are used as tags to mark the state of protein folding
Improperly folded proteins are exported from the ER and degraded in the cytosol
Misfolded proteins in the ER activate an unfolded protein response
Some membrane proteins acquire a covalently attached glycosylphosphatidylinositol (GPI) anchor
Segregate protein from other membrane protein
Most membrane lipid bilayers are assembled in the ER
Phospholipid exchange proteins help to transport phospholipids from the ER to mitochondria and peroxisomes
1.Roadmap of protein traffic 2.Signal sequences & organelle targeting 3.Organelle epigenetic control 4.Nuclear pore complex & nuclear import/export & its receptor/signal 5.The control of nuclear import during T-cell activation 6.Protein translocation process in mitochondrial membrane: TOM, TIM, OXA 7.Relationship among import of mitochondrial precursor proteins, role of energy,its hsp70. 8.Translocation of a precursor protein into the thylakoid space of chloroplasts. 9.Peroxisomal enzymes & reactions, import mechanism distinct from mitochondria & chloroplast or unique character of peroxisome 10.SER, RER preparation, SRP, ribosome and RER protein transport 11.Cotranslation & postranlation translocation in bacteria, archea, and eucaryotes 12.Hydrophobicity of membrane protein and transmembrane domain 13.Process and role of protein N-link glycosylation in RER 14.Membrane lipid bilayer assembly in ER: using example of phosphatidylcholine synthesis 15.Phospholipid transport from ER to other organelles and comparison of ER and plasma membrane Chapter 12 practice