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Chapter 5.5 Protein sorting. The Structure of Proteins.

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Chapter 5.5 Protein sorting

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Chapter 5 5 protein sorting

Chapter 5.5 Protein sorting

The structure of proteins

The Structure of Proteins

Proteins consist of one or more polypeptide chains. A polypeptide consists of a series of amino acids joined ny peptide bonds. These chains are folded in a very precise fashion and if this folding is abolished than the protein generally becomes non-functional.

Secondary and tertiary structure

Secondary and tertiary structure

Typically the three dimensional structure of a protein is composed of a series of fairly rigid sections strongly stabilised by hydrogen bonds (mainly alpha-helix and beta pleated sheet) and flexible zones.

The flexibility means that a molecule binding at one point on the surface of the protein will produce sympathetic changes at other points, in particular in the sites which bind the substrate and catalyse the reaction.

Chapter 5 5 protein sorting

5.5.1 Signal hypothesis

1 signal peptide

exist in N-protein

16-26 aa,including hydrophobic center, N-protein and C-protein


Chapter 5 5 protein sorting

  • ERER

Chapter 5 5 protein sorting

Signal hypothesis

Chapter 5 5 protein sorting

Cotrnaslocation :

Synthesis and transport occurred at the same time

Start transfer sequence:

lead peptide go through ER

Stop transfer sequence:

Stop transfer signal

stop-transfer signal

  • Hydrophobic center of peptide,peptide have one or more stop-transfer signal,it can locate middle or end of the peptide

  • N-signal peptide is start-transfer signalif located in the middle, consider internal signal peptide

Chapter 5 5 protein sorting

  • As for mitochodria and

  • Signal petide was named leader petide

    post translocation:

    after protein synthesised in the cytosol,then transferd to organelle,so refered post translocation

    In the process of protein transmembrane,need ATP to get rid of fold ,and some proteins to help to fold functional proteins

Signal recognition particle srp

(signal-recognition particle, SRP)

  • 6RNA

  • SRP


Srp srp receptor

SRPSRP receptor

(docking protein, DP)SRP-SRP

Chapter 5 5 protein sorting

5.5.2 Basic pathway and type of protein sorting

post transloction:

polypeptide completed synthesis in the cytosol,and then transfer into orther organelle


  • After Protein start synthesis,peptiede transfer to RER, protein synthesis company with tansfering to RER cavity

Protein sorting signal

protein sorting signal

1 Signal peptide

2 ER Retrivieval signal(KDEL)

3 Leader peptide for mitochondria

4 Nucleus location signal

Chapter 5 5 protein sorting

Chapter 5 5 protein sorting

Classify depend on sorting mechanism

  • Transmembrane transport

  • Vesicular transport

  • Gated transport

  • Cytosol protein sorting

Protein transmembrane transfer

Protein transmembrane transfer

  • Protein transmembrane transfer is more complex than soluble protein

  • stop-transfer peptide or halt transfer peptide locate in middle of peptide ,formed transmembrane protein

  • Single transmembrane: only one start transfer sequence and one stop transfer sequence

  • More times transmembrane:more start transfer sequence and more stop transfer sequence

Transmembrane transport

(transmembrane transport)

(protein transportor)(unfold)

Chapter 5 5 protein sorting

5.2.3 Vesicular transport Type

A Gridding protein coated vesicles

B COP coated vesicles ERGolgi

C COP coated vesicles

retrieve escaped proteins---ER

A gridding protein coated vesicles

A Gridding protein coated vesicles

  • Transport protein from TGN golgi to cytoplasm,lysosome or vacuole

  • Golgi TGN is origin of gridding protein coated vesicles

B cop coated vesicles and regulation

B COP coated vesicles and regulation

  • ER to golgi

  • COP coated vesicles select and condense transfer material

  • COP coated vesicles can recognize cytosol signal of transmembrane ER protein

    cavity of transmembrane ER protein combine with soluble protein of cavity ER

Chapter 5 5 protein sorting

  • Sar protein(a small combined GTP protein) can act as molecular switch,regulate vesicular coat

  • Sar+GDP=inactive Sar+GTP=activeSar protein combine with membrane of ERform COP coated vesicles

C cop coated vesicles

C COP coated vesicles

1 Double direction transport

Retrograde transport from Golgi to ER; anterograde transport from ER to Golgi ;

2 Main function was callback escaped protein from golgi to ER,

3 Retrieval signalLys-asp-glu-leu,or KDEL, golgi CGN can recognize retrieval signal,form COP coated vesicles to transfort to ER ,If protein was short of retrieval,protein cannot come back to ER

4 ER is Open prison

Chapter 5 5 protein sorting

Many ER-resident protein bear a C-Terminal KDEL

Maily located in cis golgi network and ER-to GOLGI trasport vesicle

Chief function is bing proteinwith KDELand return them to ER

Chapter 5 5 protein sorting

Cop vesicle coat regulation

COPvesicle coat regulation

  • ARF +GDP=inactive ARF +GTP=active

  • ARF change depend on GNRP()and GAP (GTP )

  • GNRP let ARFrelease GDPand combine with GTPARF becomed activeregulated COPvesicle coat

  • GAP trigger ARF hydrolyze GTP into GDP ARF becomed inactiveCOP, COPvesicle coat disaggregationvesicle fused with target membrane

Chapter 5 5 protein sorting Transport vesicle formation

1 Selective fusion is the key factor for directional protein trasport.vesicle from ER only fused with cis CGN()

2 Rough ER is material source ,and golgi is important distributing center

3 ER is Open prison

Leader peptide

leader peptide

  • ATPHsp70

Molecular chaperone

(molecular chaperone)

  • (bindin protein,BiP)

  • Hsp60

Chapter 5 5 protein sorting


Chapter 5 5 protein sorting

5.5.4 Cell assemble system

Self assemble

Aid assemble

Direct assenble

Chapter 5 5 protein sorting

  • Cell assemble function

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