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Targeting of Proteins to the Organelles

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Presentation on theme: "Targeting of Proteins to the Organelles"— Presentation transcript:

1 Targeting of Proteins to the Organelles

2 Targeting of Proteins: Nucleus and Mitochondria

3 The Nucleus Central Dogma Functions

4 Proteins are made in cytoplasm-transported to other locations
Central dogma: DNA--> RNA--> Protein Nucleus Cytoplasm nucleus mitochondria Rough endoplasmic reticulum (ER) Fig 13.1 animation

5 The Nucleus Structures Nuclear Envelope Nuclear Lamina Nuclear Matrix
Chromosomal Domains Nuclear Pore Complex Houses DNA Organized Regulated movements

6 The Nucleus Nucleus holds DNA
Keeps DNA organized throughout the cell life cycle The nucleus is organized similar to a mini-cell within a cell

7 The Nucleus: DNA organization Chromatin Discrete DNA localization

8 The Nucleus: Nuclear Lamina
Supportive mesh on the inside of the nuclear envelope Nuclear Matrix Provides a structured space

9 The Nucleus The Nuclear Envelope is a continuous membrane that forms a double bilayer Outer: Inner:

10 The Nucleus: Nuclear Pore Complex
How do molecules get into the nucleus? Nuclear Pore complex

11 Nuclear Pore Complex Cytoplasmic Nucleoplasm
Here is an electron micrograph of the NPC. Regulates movement of proteins between cytoplasm and nucleus

12 The Nucleus: Nuclear Pore Complex
The NPC is one of the largest protein complexes in the cell Composed of: Limited diffusion: Membrane bound:

13 The Nucleus: Nuclear Pore Complex
Basket portion on the nucleoplasm side is joined by filaments

14 The Nucleus: Nuclear Pore Complex
Center of the nuclear pore is aqueous Imported proteins move through the NPC via a brownian gate model

15 The Nucleus: Nuclear Pore Complex
Some channel and basket nucleoporins form hydrophobic stretches Structural Nups:

16 NPC Structure Cytoplasmic Nups Symmetric Nups Nuclear Nups

17 Nuclear Import and Export
Many proteins are too large to pass through the NPC alone How does this occur?

18 Nuclear Import PLAYERS Cargo Proteins Import Proteins Ran Ran-GEF

19 Nuclear Import Importins Exportins FG repeats

20 Nuclear Import Importins can form a heterodimeric nuclear import receptor Ran

21 Nuclear Import Free Importin binds to NLS in the cytoplasm

22 Nuclear Import Upon entering the nucleus, importin interacts with Ran-GTP

23 Nuclear Import Ran-GTP/Importin complex then diffuses out of the nucleus Ran-GAP

24 Nuclear Import Ran GDP returns to nucleus through NPC Ran-GEF

25 Ran: GTPase in Nuclear Transport
G protein switches Two confirmations GTP-bound GDP-bound GTPase hydrolyzes GTP to GDP; slow enzyme Modifying Proteins Guanine nucleotide exchange factors (GEF) GDP GTP Nuclear GTPase Activating Protein (GAP) ***this protein is not a GTPase!! GTP GDP Cytoplasmic

26 Nuclear Import Diffusion through the pores is random, but transport is directional How is this achieved?

27 Nuclear Export Exportin binds to cargo

28 Nuclear Export Ran-GTP makes contact with Ran-GAP in cytoplasm
Complex dissociates

29 Nuclear Import and Export
Both use Ran-GTP Import: Export:

30 Nuclear Import

31 How are proteins targeted to the nucleus?
Nuclear Transport Proteins Imported Proteins DNA replication DNA repair Transcription Unassembled ribosome Exported Proteins mRNA (bound to proteins) tRNA (bound to proteins) Assembled ribosome How are proteins targeted to the nucleus?

32 Signal Sequence: Cellular Address
Barack Obama 1600 Pennsylvania Avenue Washington, D.C

33 Signal Sequences NLS

34 Signal Sequences Signal sequences direct the final protein destination
Chemical properties of the amino acids in the sequence direct interactions

35 Signal Sequences These sequences are read by specific transport receptors K—Lysine R--Arginine

36 Nuclear Localization Signal
Pro-Lys-Lys-Lys-Arg-Lys-Val Digitonin

37 Nuclear Export Signal Used to transport proteins, tRNA, ribosomal subunits out of the nucleus Exportins bind the NES to start the process

38 Mitochondria Power house of cell Outer membrane simple bilayer
permeable to ions and small molecules Inner membrane IMPERMEABLE to all material except through carrier channels Complex in conformation Contains all electron transport chain machinery Contains all ATP synthesis machinery

39 Mitochondria Power house of cell Intermembrane space
Complex shape (follows contours of inner membrane pH ~7 Matrix all enzymes required for Krebs cycle Hold mitochondrial genome, ribosomes, enzymes for mitochondrial division pH ~8

40 Mitochondria Mitochondria harness energy Glycolysis (pyruvate)
Generate ATP

41 Mitochondria cellular respiration
“Breathing” on a cellular level Occurs in the inner membrane and the inner membrane space membrane surface area

42 Electron Transport Chain

43 Mitochondria Matrix contains all necessary components for mitochondrial replication Mix of mitochondrial encoded proteins and those from the nuclear genome

44 Signal Sequences

45 Mitochondrial targeting sequences
The signal for matrix mitochondrial proteins is part sequence, but also part structure Amphipathic Receptors that bind the sequences can bind to more than one specific sequence

46 Mitochondrial Protein Transport
Transport of proteins in to the mitochondria requires: Transport occurs:

47 Mitochondrial Protein Transport
Players Hsc70 Chaperones Outer membrane Translocon Outer membrane receptors- Tom 20/22 or Tom 70/22 Outer membrane channel- Tom 40 Inner membrane Translocon Inner membrane channel- Tim 23/17 Matrix Proteases

48 Mitochondrial Protein Transport
Chaperones (HSC 70) keep proteins unfolded

49 Mitochondrial Protein Transport
Precursor binds to the import receptor on the outer membrane Import receptors: Tom 20/22

50 Mitochondrial Protein Transport
Transport to the matrix occurs simultaneously Tim23/17 mediate transport to the matrix

51 Juxtaposition of Inner and Outer Membranes at Transport Sites

52 Mitochondrial Protein Transport
Cytosolic Hsc70 keeps precursor Protein in partially unfolded state Tom20/22 Receptor recognized matrix-targeting sequence Transfer of Precursor through Tom40 channel Passes through Tim23/17 channel Matrix Hsc70 helps pull precursor through channel Matrix protease cleaves off signal sequence

53 Mitochondrial Transport Movie

54 Transport of Mitochondrial Membrane Proteins

55 Stop-Transfer Players Tom20/22 Tom40 Tim23/17 Tim44 Hsc70
Matrix Protease

56 Stop-Transfer Process same as with Matrix-targeted protein
Have Matrix targeting sequence BUT Internal Stop-Transfer sequence recognized by Tim23/17 channel Sequence is hydrophobic Precursor is transferred into the inner membrane bilayer

57 Path B Proteins contain a matrix targeting sequence and internal hydrophobic domains Oxa1 Tom40, Tim23/17 are involved in transport

58 Path C Proteins do not contain a matrix targeting sequence
Recognized by the Tom70/22 complex

59 Intermembrane Space Localization

60 Path A Major Pathway Proteins contain a matrix targeting sequence
Translocation to the matrix begins

61 Path B Some proteins can just move through Tom40

62 Outermembrane proteins
Like Tom40 itself Proteins interact with Tom40 Then transferred to the SAM complex (sorting and assembly machinery)

63 Section assignments for next week
Undergraduate Read article on Ran in Nuclear Transport Graduate Read article on Tubular ER network

64 Problem Set 1 Undergraduates Problem Set 1 will be posted on Friday
Due Feb 28th by

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