Lect5_protSort4

Lect5_protSort4 - Protein sorting continued ER-localized...

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1 Protein sorting continued ER-localized processes Vesicular transport Recommended reading: MBOC 704-712, 723-745 F09 D103 Cell Biology - lecture 12 © Gross- all rights reserved.
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How are proteins imported into the ER? ER signal : 6-12 hydrophobic aa preceded by one or two basic (+) aa Receptor: signal-recognition particle (SRP) receptor Translocation machinery : translocons in ER membrane Translocation powered by: GTP-hydrolyzing proteins (SRP and SRP- receptor) and energy released during translation 2 F09 D103 Cell Biology - lecture 11 © Gross- all rights reserved.
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Protein transport into ER is not always co- translational 3 Core of the Protein translocator complex Remember hsp70 in mitochondria? F09 D103 Cell Biology - lecture 11 © Gross- all rights reserved.
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Translocation soluble protein • ER signal sequence (start transfer sequence) Translocation of a single-pass transmembrane protein • ER signal sequence (start-transfer signal) stop-transfer sequence (hydrophobic, serves as transmembrane domain) (NOTE: signal sequence is cleaved) 4 F09 D103 Cell Biology - lecture 11 © Gross- all rights reserved.
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Translocation of a single-pass transmembrane protein (with an internal signal sequence) Orientation of insertion of signal-anchor sequence determined by high density of positively charged amino acids adjacent to hydrophobic sequence. Positively charged residues remain on cytosolic side membrane. 5 Type II protein Type I protein +-charged aa: Arginine (Arg, R),Lysine (Lys,K), Histidine (His, H)
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Compare internal signal sequence and N-terminal ER-localization signal seq 6 Similarities: •Both dominated by hydrophobic amino acids (e.g.alanine (Ala), glycine (Gly), Valine (Val), leucine (Leu), etc.) •Both have a few positive AA close to the hydrophobic AA. • Both α-helix • Both recognized and delivered by SRP Differences: • N-terminal: positive aa on N-terminal side of hydrophobic aa; internal: positive aa on either side •Different length: internal 20-30 aa long, N-terminal 6-12 aa •Internal NOT cleaved off—spans membrane; N-terminal cleaved F09 D103 Cell Biology - lecture 12 © Gross- all rights reserved.
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Combinations of start-transfer and stop-transfer signals determine topology of multipass transmembrane proteins 7 F09 D103 Cell Biology - lecture 11 © Gross- all rights reserved.
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8 Review: Diverse groups of membrane proteins lumen cytosol Multiple helices Multiple -sheets • C in cytosol (type I) • C in lumen (type II) single helix Lipid- anchored peripheral GPI- anchored Peripheral membrane proteins Cytosolic side only exoplasmic side only integral membrane proteins F09 D103 Cell Biology - lecture 11 © Gross- all rights reserved.
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Properties of a typical trans-membrane domain •Dominated by hydrophobic amino acids (e.g.alanine (Ala), glycine (Gly), Valine (Val), leucine (Leu), etc.) (see Fig 3-2, properties of the AA) • Typically an α-helix •Usually 20-30 aa long •Can frequently be identified in hydropathy plot; such
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This note was uploaded on 12/13/2011 for the course BIOSCI d103 taught by Professor Staff during the Fall '11 term at UC Irvine.

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Lect5_protSort4 - Protein sorting continued ER-localized...

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