Cellular Transport. 1. Transport to and across the membrane 1a. Transport of small molecules and ions 1b. Transport of proteins

Transcription

1 Transport Processes

2 Cellular Transport 1. Transport to and across the membrane 1a. Transport of small molecules and ions 1b. Transport of proteins 2. Vesicular transport 3. Transport through the nuclear membrane

3 1a. Transport of small molecules and ions

4 1 Membrane permeability Extracellular space Small hydrophobic molecules and gases O 2 CO 2 N 2 benzene Small polar molecules H 2 O glycerol alcohol Cell membrane Cytoplasm Large polar molecules Amino acids glucose nucleotides Ions Na + K + HCO3 - Ca 2+ Cl - H + Mg 2+ Cell membrane

5 2 Membrane transport passive transport active transport diffusion facilitated diffusion uniporter cotransporters symporter antiporter

6 Concentration gradient (= chemical gradient) 3

7 Electro-chemical gradient 4 Electrochemical gradient: 1. Electric gradient 2. Concentration gradient

8 Carrier proteins (transporters) Passive transport 5 Facilitated diffusion: (1) carrier proteins: e.g. glucose transporter (2) channels: e.g. aquaporin and ion channels glucose Glucose transporter Cell membrane 12 transmembrane segments

9 Passive transport 6 Channel proteins Aquaporin (water channel) 6 transmembrane segments homotetramer 2003 Peter Agre: for the discovery of water channels

10 Passive transport 7 Ion channels Voltage-gated ligand-gated stress-gated Outer ligand inner ligand CLOSED 2003 OPEN Roderick MacKinnon: for structural and mechanistic studies of ion channels

11 Passive transport 8 Voltage-gated channels Na + - channel Voltage sensor Pore

12 Active transport Proteins of active transport 9 1. ATP-gated: - Na + /K + pump, Ca 2+ pump, ABC transporters (primary active transport) 2. Ion gradient-gated: - Na + /Ca 2+ pump (secondary active transport) Na + /K + pump

13 Active transport Proteins of active transport ATP-gated: - Na + /K + pump, Ca 2+ pump, ABC transporters (primary active transport) 2. Ion gradient-gated: - Na + /Ca + pump (secondary active transport) ABC transporter extracellular space cytoplasm ATP binding ATP cleavage P i release ATP binding casette

14 1b. Protein transport

15 Protein transport 1a.

16 1b. The main protein transport pathways

17 ER - Signal sequence 1 5 Ribosome cytoplasm mrns Signal peptide 3 mrna 4. cytoplasm 3 SRP Receptor Signal peptidase 3 2. Rough ER 1. SRP Signal recognition particle SRP Receptor ER lumen 5. Protein ER membrane Nobel Prize Signal sequences in the proteins ER lumen Protein S 30S Günter Blobel 3. Signal peptidase 7. Protein

18 Protein transport to 3. the ER

19 Structure of the signal recognition particle (SRP) 4. P54 P19 Binds ER signal sequence P68 P72 7SL RNS Provides a scaffold for the assembly of SRP Required for protein translocation P9 P14 Interact with ribosomes

20 Protein modification in the 5. ER glycosylation Modifications: 1. Glycosylation 2. Disulfide bridge formation 3. Protein folding GlcNAc: N-acetylglucosamine Man: mannose Glc: glucose conserved variable Asn: N-linked oligosaccharide Ser or Thr: O-linked oligosaccharide

21 Protein folding in the ER 6. Proteins involved in protein folding: 1. chaperon: BiP 2. Lectines: calnexin, calreticulin 3. PDI: disulfide bridge formation 4. Oligosaccharyl transferase: glycosylation 5. Peptidylprolyl isomerase: prolin cis-trans transformation

22 Topological classes of the integral proteins 7. Cytosol TYPES: I. II. III. IV. Cut signal sequence Exoplasmic space (lumen, cytoplasm membrane, extracellular space)

23 Insertion of type I integrant proteins to the ER membrane 8.

24 Insertion of type II integrant proteins to the ER membrane 9.

25 10. Arrangement of topogenic sequences Type IV membrane proteins: multiple topogenic sequences

26 Phospholipid anchors Mobile proteins

27 Transport to the mitochondrial matrix citoszól Tom: translocon of the outer membrane Tim: translocon of the inner membrane Folding: spontaneous or chaperonin-mediated

28 13. Localization of the targeting sequences On the imported mitochondrial proteins

29 Transport from the cytosol to the inner 14. mitochondrial membrane

30 Transport from the cytosol to the mitochondrial intermembrane space 14.

31 2. Vesicular Transport

32 Secretory endocytic pathways 1.

33 Vesicle budding and fusion 2.

34 3. Docking and fusion of transport vesicles with their target membranes

35 3. Transport to the nucleus

36 Protein transport to the nucleus 1 IMPORT NLS cargo protein Ran Ran Importin RCC1 NUCLEOPLASM Nuclear membrane CYTOPLASM Ran Nuclear pore complex Nuclear membrane cargo protein Importin Importin Ran Ran GAP Importin cargo protein NLS Importin Importin Ran

37 Protein transport from the nucleus EXPORT 2

38 mrna transport from the nucleus 3 EXPORT