Aquaporins: transmembrane channels that allow rapid movement of water across plasma membrane in various cells--erythrocytes proximal renal tubule cells table 12-3 Aquaporins Aquaporin Roles and location AQP-1 Fluid reabsorption in proximal renal tubule secretion of aqueous humor in eye and cerebrospinal fluid in central nervous system; water homeostasis in lung AQP-2 Water permeability in renal collecting duct (mutations produce nephrogenic diabetes insipidus) AQP-3 Water retention in renal collecting duct AQP-4 Reabsorption of cerebrospinal fluid in central nervous system regulation of brain edema AQP-5 Fluid secretion in salivary glands, lachrymal glands, and alveolar epithelium of lung TIP Water uptake by plant vacuole, regulating turgor pressure Source: King, L.S.& Agre, P(1996)Pathophysiology of the aquaporin water channels Annu. Rev. Physio/ 58, 619-648
Aquaporins: transmembrane channels that allow rapid movement of water across plasma membrane in various cells—erythrocytes, proximal renal tubule cells
Transmembrane topology of an aquaporin, AQP ype Outside 回的9 00000o收p图000 Inside HSN 4 cOo- a tetramer Flow rate: 5x10/sec, better than the best enzyme catalyse(4x10 /s) AG<15kJ/mol: continuous stream, not much interruption
Transmembrane topology of an aquaporin, AQP-1 Type III A tetramer Flow rate: 5x108 /sec, better than the best enzyme catalyase (4x107 /s) DG<15kJ/mol: continuous stream, not much interruption
Glucose transporter of erythrocytes(GluT1): plasma conc=5 mM transporter-50,000 more efficient than simple diffusion O Hydrophobic O Polar O Charged Outside Inside tNHa COO
Glucose transporter of erythrocytes (GluT1): plasma conc=5 mM; transporter—50,000 more efficient than simple diffusion
-Ser-Leu-Val-Thr-Asn-Phe-Ile eu 5 Helical Wheel diagram 6 Asn Phe Distribution of polar Vs nonpolar residues hydrophobic amphipathic helix(one 1 Ser side hydrophobic, the other hydrophilic) hydrophilic Thr Ile 4 (b)
Helical Wheel Diagram: Distribution of polar vs nonpolar residues— amphipathic helix (one side hydrophobic, the other hydrophilic) hydrophobic hydrophilic
Formation of a channel by side-by-side association of 5 or 6 amphipathic helices Hydrogen bonds
Formation of a channel by side-by-side association of 5 or 6 amphipathic helices Hydrogen bonds