Transport Processes
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
1a. Transport of small molecules and ions
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
2 Membrane transport passive transport active transport diffusion facilitated diffusion uniporter cotransporters symporter antiporter
Concentration gradient (= chemical gradient) 3
Electro-chemical gradient 4 Electrochemical gradient: 1. Electric gradient 2. Concentration gradient
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
Passive transport 6 Channel proteins Aquaporin (water channel) 6 transmembrane segments homotetramer 2003 Peter Agre: for the discovery of water channels
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
Passive transport 8 Voltage-gated channels Na + - channel Voltage sensor Pore
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
Active transport Proteins of active transport 10 1. 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
1b. Protein transport
Protein transport 1a.
1b. The main protein transport pathways
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 5 3 3 Nobel Prize Signal sequences in the proteins 2. 6. ER lumen Protein 1999 3 50S 30S Günter Blobel 3. Signal peptidase 7. Protein
Protein transport to 3. the ER
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
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
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
Topological classes of the integral proteins 7. Cytosol TYPES: I. II. III. IV. Cut signal sequence Exoplasmic space (lumen, cytoplasm membrane, extracellular space)
Insertion of type I integrant proteins to the ER membrane 8.
Insertion of type II integrant proteins to the ER membrane 9.
10. Arrangement of topogenic sequences Type IV membrane proteins: multiple topogenic sequences
Phospholipid anchors Mobile proteins
Transport to the mitochondrial matrix citoszól Tom: translocon of the outer membrane Tim: translocon of the inner membrane Folding: spontaneous or chaperonin-mediated
13. Localization of the targeting sequences On the imported mitochondrial proteins
Transport from the cytosol to the inner 14. mitochondrial membrane
Transport from the cytosol to the mitochondrial intermembrane space 14.
2. Vesicular Transport
Secretory endocytic pathways 1.
Vesicle budding and fusion 2.
3. Docking and fusion of transport vesicles with their target membranes
3. Transport to the nucleus
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
Protein transport from the nucleus EXPORT 2
mrna transport from the nucleus 3 EXPORT