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Chapter 12 Intracellular Compartments and Protein Sorting 張學偉 助理教授.

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Presentation on theme: "Chapter 12 Intracellular Compartments and Protein Sorting 張學偉 助理教授."— Presentation transcript:

1 Chapter 12 Intracellular Compartments and Protein Sorting 張學偉 助理教授

2 The compartmentalization of cells

3 All eucaryotic cells have the same basic set of membrane-enclosed organelles

4 The major intracellular compartments of an animal cells.
Cytoplasma = cytosol + cytoplasmic organelles




8 The topological relationships of membrane-enclosed organelles can be interpreted in terms of their evolutionary origins





13 Protein can move between compartments in different ways

14 Sorting signal by signal sequences

15 Vesical transport

16 Signal sequences and signal patches direct proteins to the correct cellular address

17 Sorting signal (signal sequences) recognize by sorting receptors
Cut by signal peptidases Sorting signal (signal sequences) recognize by sorting receptors

18 Red + Green  - Yellow Hydrophobic Blue  hydroxylated N-terminal signal C-terminal signal




22 The transport of molecules between the nucleus and the cytosol


24 Nuclear pore complexes perforate the nuclear envelope

25 Composed by more than 50 different proteins
called nucleoporins.



28 26nm 15nm 9nm size

29 Nuclear localization signals (NLS) direct nuclear proteins to the nucleus


31 Nuclear pore transport (large aqueous pore) is
Colloidal gold spheres coated with peptides containing NLS Nuclear pore transport (large aqueous pore) is fundmental different from organelle transport (lipid bilayer).

32 Nuclear import receptors bind nuclear localization signals and nucleoporins

33 FG-repeat (Phe-Gly) serve as binding sites for the import receptors.
Nuclear import do not always bind to nuclear proteins directly. Soluble cytosolic protein FG-repeat (Phe-Gly) serve as binding sites for the import receptors.

34 Nuclear export works like nuclear import, but in reverse
Nuclear export signals & nuclear export receptor & nuclear transport receptor (karypherins) tRNA or 5S RNA: nuclei cytosol NLS-particle: cytosol nuclei

35 The Ran GTPase drives directional transport through nuclear pore complexes

36 Ran = GTPase GAP = GTPase-activing protein GEF = Guanine exchange factor

37 Bidirectional model



40 Transport between the nucleus and cytosol can be regulated by controlling access to the transport machinery Always in & out, shuttling

41 Ventral side Dorsol protein The control fly embryo development by nuclear transport


43 The nucleus envelope is disassembled during mitosis

44 Lamina (whole structure) & lamins (protein subunit)


46 The transport of proteins into mitochondria and chloroplasts


48 Newly mito & chloropl are produced by the growth of
preexisting organelle. Their growth depends mainly on the cytosolic protein import

49 Translocation into the mitochondrial matrix depends on a signal sequence and protein translocators

50 Red = + Yellow = nonpolar On different side Amphipathic a helix

51 translocase Transport to matrix Insert to inner memb. For protein syn
Require for import all nucleus-encoded mitochondria protein Transport to matrix Insert to inner memb. For protein syn In mito

52 Interacting protein: eg Charperone protein  hsp70 family
All Interacting protein help to prevent aggregation before engaging with TOM complex in outer mito membrane. Mitchondrial precursor proteins are imported as unfolded polypeptide chains

53 Mitochondrial precursor proteins are imported into the matrix at contact sites that join the inner and outer membranes


55 Protein import by mitochondria

56 ATP hydrolysis and a H+ gradient are used to drive protein import into mitochondria

57 Charperone protein also function as translocator
Freely permeable to ions and metabolites but not to most protein pulling Charperone protein also function as translocator

58 Repeated cycles of ATP hydrolysis by mitochondrial Hsp70 complete the import process.
Hsp 60 provide chamber for unfolded polypeptide chain facilitates folding (chapter 6)



61 Protein transport into the inner mitochondrial membrane and the intermembrane space required two signal sequences



64 Two signal sequences are required to direct proteins to the thylakoid membrane in chloroplasts
Resemble in mitochondria



67 peroxisomes


69 Peroxisomes use molecular oxygen and hydrogen peroxide to perform oxidative reactions

70 Catalase: 2H2O2 2H2O + O2 Urate oxidase: RH2 + O2 R + H2O2 Animal: b-oxidation occur at both mitochondria & perixosome. Plant & yeast: b-oxidation occur only at perixosome.

71 Plasmalogen the most abundant protein in myelin. deficient result in neurological disease. Animal Perxisome catalyze the first step for plasmalogen biosyn

72 Glyoxylate cycle

73 A short signal sequence directs the import of proteins into peroxisomes

74 Most peroxisomal membrane proteins are made in the cytosol
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.

75 The endoplasmic reticulum


77 Membrane-bound ribosomes define the rough ER


79 Many ribosomes bind to a single mRNA


81 ER capture 2 type of protein:
Cotranslatioal transport? Posttranslational transport? ER capture 2 type of protein: transmembrane protein & water-sol protein

82 In mammalian cells Compared to page 697 p690 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)

83 Smooth ER abundant in some specialized cells

84 Lipid metabolism (cholestersol)
Detoxification by cytochrome p450 Sequester Ca+2 from cytosol (SR) Autophagocytosis & phenobarital

85 Rough and smooth regions of ER can be separated by centrifugation


87 Cell-free system

88 Signal sequences were first discovered in proteins imported into the rough ER


90 A signal-recognition particle (SRP) directs ER signal sequences to a specific receptor in the rough ER membrane


92 ER & SRP for import


94 The polypeptide chain passes through an aqueous pore in the translocator



97 Translocation across the ER membrane does not always require ongoing polypeptide chain elongation

98 p693 rare

99 Protein that are are first released into cytosol (bind to hsp to prevent folding) ATPase c/o sealing the pore Binding protein (hsp70-like chaperone protein) yeast

100 The ER sequence is removed from most soluble proteins after translocation

101 Start-transfer signal

102 In single-pass transmembrane proteins, a single internal ER signal sequence remains in the lipid bilayer as a membrane-spanning of a helix



105 Combinations of start-transfer and stop-transfer signals determine the topology of multipass transmembrane proteins



108 hydrophobicity

109 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)

110 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.

111 O-linked oligosaccharide are found in Golgi.
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.



114 Oligosaccharides are used as tags to mark the state of protein folding


116 Improperly folded proteins are exported from the ER and degraded in the cytosol

117 Retrotranslocation (dislocation) deglycosylation

118 Misfolded proteins in the ER activate an unfolded protein response


120 Some membrane proteins acquire a covalently attached glycosylphosphatidylinositol (GPI) anchor

121 Segregate protein from other membrane protein

122 Most membrane lipid bilayers are assembled in the ER





127 Phospholipid exchange proteins help to transport phospholipids from the ER to mitochondria and peroxisomes


129 Chapter 12 practice Roadmap of protein traffic
Signal sequences & organelle targeting Organelle epigenetic control Nuclear pore complex & nuclear import/export & its receptor/signal The control of nuclear import during T-cell activation Protein translocation process in mitochondrial membrane: TOM, TIM, OXA Relationship among import of mitochondrial precursor proteins, role of energy,its hsp70. Translocation of a precursor protein into the thylakoid space of chloroplasts. Peroxisomal enzymes & reactions, import mechanism distinct from mitochondria & chloroplast or unique character of peroxisome SER, RER preparation, SRP, ribosome and RER protein transport Cotranslation & postranlation translocation in bacteria, archea, and eucaryotes Hydrophobicity of membrane protein and transmembrane domain Process and role of protein N-link glycosylation in RER Membrane lipid bilayer assembly in ER: using example of phosphatidylcholine synthesis Phospholipid transport from ER to other organelles and comparison of ER and plasma membrane

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