PTW - Transporters Flashcards
(19 cards)
Q: What are membrane transporters, and how do they function? (3)
- Move molecules inward or outward across membranes
- Transition between outward-facing, inward-facing, and occluded states
- Show high or low substrate affinity and use symport (same direction) or antiport (opposite directions)
Q: What are solute carrier proteins (SLCs) and their functions? (3)
- Over 50 subfamilies, \~300 proteins
- Involved in nutrient uptake, drug elimination, vesicle loading, and neurotransmitter reuptake
- Therapeutic targets in neurology, diabetes, and diuretic therapy
Q: What are two major SLC structural families, and how do they differ? (2)
- Major Facilitator Superfamily: 12 TMDs, inverted repeats (e.g. GLUT for glucose)
- LeuT family: 10 TMDs, Na⁺/Cl⁻ symporters (e.g. neurotransmitter transporters)
Q: How are SLC transporters involved in CNS function and disease? (2)
- Handle uptake of glutamate and monoamines
- Key targets in epilepsy, depression, schizophrenia, autism
Q: What powers vesicular neurotransmitter transporters? (2)
- H⁺ gradient generated by vATPase
- Uses ΔpH and/or Δψ depending on substrate type
Q: How do vesicular transporters differ by neurotransmitter type? (3)
- Cations (e.g. ACh): Use ΔpH (H⁺ exchange)
- Zwitterions (e.g. GABA, Gly): Use both ΔpH and Δψ
- Anions (e.g. Glu): Use primarily Δψ
Q: How does vesicular glutamate transport work? (3)
- Uses Cl⁻ exchange to balance charge
- Active at low pH (vesicle), inactive at neutral pH (plasma membrane)
- Regulated allosterically by H⁺
Q: What are SLC6 transporters, and what is their clinical relevance? (2)
- Found in CNS and peripheral tissues
- Targets in depression, epilepsy, schizophrenia; structure studied via LeuT
Q: What is the structure of SLC6 family transporters? (2)
- 12 transmembrane domains, twofold symmetry
- Ligand binding coordinated with Na⁺/Cl⁻
Q: What is the function and clinical relevance of the serotonin transporter (SERT)? (3)
- Transports serotonin (5-HT) to terminate synaptic signalling
- Powered by Na⁺/Cl⁻ gradient
- Target for SSRIs and addiction treatments like ibogaine
Q: What are challenges in transporter structure determination? (2)
- Membrane proteins are unstable in detergents
- Stabilised using thermostable mutations and Fab fragments for crystallisation
Q: Describe the architecture of SERT. (2)
- Na⁺/Cl⁻ ions form part of the substrate binding site
- Substrate and drug binding are coupled to ion movement
Q: How do antidepressants act on SERT? (2)
- Bind the central substrate binding cavity
- Lock transporter in outward-open conformation
Q: Which drugs target SERT, and what are their characteristics? (3)
- SSRIs: Sertraline, Fluvoxamine, Paroxetine
- Ibogaine: Inhibitor used in addiction treatment
- Antidepressants show high affinity (Ki 2–10 nM) and bind 3 subsites
Q: What technique reveals the catalytic transport cycle? (2)
- Cryo-EM shows outward → occluded → inward transitions
- Resolution \~4.1 Å; stabilised using ibogaine and Fab fragments
Q: How is gating controlled in transporter function? (2)
- Substrate movement controlled via outward/inward vestibule gates
- Allosteric regulation locks conformation to prevent dissociation
Q: What are challenges and uses of cryo-EM in drug design? (2)
- Key for membrane proteins, but limited by moderate resolution
- Higher resolution needed to define substrate and sidechain interactions
Q: What is the role of the allosteric site in transporter regulation? (4)
- Located near TM1, TM6b, TM10–11, EL4, EL6
- Flexible binding site, occludes substrate pocket
- Enables diverse inhibitor design
- Regulates substrate dissociation
Q: Summarise the key features of SLC transporters. (4)
- Diverse family in uptake, neurotransmission, and drug response
- Vesicular transport driven by proton motive force
- Plasma membrane transporters driven by ion gradients
- Structure, conformational cycling, and binding specificity are key for drug targeting
