Gene expression

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GCCTCAATGGATCCACCACCCTTTTTGGGCAGCCTCAATGGATCCACCAC
CCTTTTTGGTGCAAGCCTCAATGGATCCACCACCCTTTTTGGTGCAAGCC
TCAATGGATCCACCACCCTTTTTGGTGCAAGCCTCAATGGATCCACCACC
CTTTTTGGTGCAAGCCTCAATGGATCCACCACCCTTTTTGGTGCAAGCCT
CAATGGATCCACCACCCTTTTTGGTGCAGCCTCAATGGATCCACCACCCT
TTTTGGGCAGCCTCAATGGATCCACCACCCTTTTTGGTGCAAGCCTCAAT
GGATCCACCACCCTTTTTGGTGCAAGCCTCAATGGATCCACCTCCACCAC
CCTTTTTGGTGCATGTGCCATGGC
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(No Transcript)
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• Gene expression
• Transcription
• Translation
• Functional proteins post-translational
  modifications
• Phosphorylation
• Glycosylation
• Sorting targeting to appropriate organelles
• Modulation by extracellular signals
• Covalent modification
• Association with other molecules
• Degradation

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Sorting and Secretory pathways

• diverged in trans-Golgi
• Constitutive pathway
• many soluble proteins
• Regulated pathway
• stored in secretory vesicles
• active transport from cytosol to vesicles
• complexed with macromolecules (e.g. proteglycans)

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Regulated secretory pathway

• In response to extracellular stimuli hormone,
  transmitters, digestive enzymes
• stored in secretory vesicles
• active transport from cytosol to vesicles
• complexed with macromolecules (e.g. proteglycans)
  to reach high concentration

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(No Transcript)
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Three pathways in Golgi

• to lysosome
• with mannose-6-phosphate, via late endosome to
  lysosome
• to secretory pathways
• Constitutive to apical or basolateral domain
• Regulated

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Roadmap for traffic

• Transport
• Gated transport cytosol and nucleus via nuclear
  pore complexes
• Membrane transport via membrane-bound
  translocators unfolded
• Vesicle transport vesicles
• Sorting signals

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Membrane transport

• Membrane-bound translocators
• Unfolding of protein to be transported
• Passing through a topologically distinct space
  cytosol to ER cytosol to mitochondria

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Equivalent space for transport

• Cycles of budding and fusion permits transport of
  molecules

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Sorting signals

• Signal sequences
• 15-60 aa
• Removed by signal peptidase when reaching the
  target
• Signal patch
• Usually non-continuous stretch of sequences
• Exposed when appropriately folded

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Sorting signals
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Signal sequences

• Function specify the direction for destination
• for initial transfer to the ER with a signal
  sequence at N-terminus consisting of 5-10
  hydrophobic aa
• Go forward Golgi most proteins
• Return to ER (ER residents) with a specific
  sequence of 4 aa at C-terminus
• Go to mitochondria positively charged amino
  acids alternate with hydrophobic ones
• Go to peroxisome with a signal peptide of 3
  characteristic at C terminus

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Signal sequences
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Experiments to demonstrate zip code

• Swap the signal sequence
• e.g. adding the ER signal sequences to a
  cytosolic protein results in the retention of
  this protein in ER
• Hyprophobicilty maybe a determing factor of
  signal sequences

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Günter Blobel
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Effect of misdirected protein
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Overview of protein sorting
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Protein sorting

• ER
• ER-Golgi intermediate
• Glogi network

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Glycosylation in ER
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Lysosomal protein phosphorylation of mannose
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Sorting in Golgi

• Export
• Lysosome
• Secretion
• Constitute
• Regulated
• Retain in Golgi
• transmembrane

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Transport to plasma membrane

• TGN
• Apical domain
• Basolateral domain

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Endocytosis

• Phagocytosis (cell eating)
• Ingestion of large particles (e.g. bacteria)
• In specialized cells
• Pinocytosis (cell drinking)
• Up-take of fluids or macromolecules in small
  vesicles
• Receptor-mediated endocytosis
• Common among eukaryotic cells

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Phagocytosis

• Pseudopodia
• Phagosome
• Phagolysosome

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Receptor-mediated endocytosis

• Clathrin-coated pits
• Clathrin-coated vesicles
• Example cholesterol, LDL, LDL receptor

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LDL low density lipoprotein

• Core
• 1500 Cholesterol ester
• Coat
• 500 cholesterol
• 800 phospholipid
• 1 Apoprotein B100

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LDL receptor

• MS Brown, JL Goldstein
• Familial hypercholesterolemia
• LDL-binding domain
• Internalization signal

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LDL receptor

• Internalization signal Tyr

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Clathrin-coated pits
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Lysosomal proteins in clathrin-coated pits
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Sorting in early endosome

• Acidic ph by H pump for dissociation of proteins

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Recycling of synaptic vesicles
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Protein sorting by transcytosis

• Membrane protein in apical domain
• Secretory proteins from bloodstream

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Lysosomal system

• For membrane-bound proteins and proteins taken by
  endocytosis
• Multiple acid proteases (cathepsins) and other
  hydrolases
• Studied with weak bases to inhibit lysosomal
  acidification or lysosomal inhibitors (E64)