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#water channels

2 public questions tagged with this topic.

Plasma Membrane Proteins

Which of the following sequences is highly conserved in Aquaporins?

Highly conserved sequence motif in aquaporin family defines aqueous pore architecture and selectivity. Loop B half-helix and Loop E half-helix each dip into membrane from opposite sides each containing invariant tripeptide Asn-Pro-Ala forming two NPA boxes meeting at center of channel creating electrostatic barrier and orienting water molecules in opposite NPA asparagine carbonyl hydrogen bond donors. Proline introduces kink allowing asparagine side chain to project into pore, alanine stabilizes packing between half-helix and transmembrane helices. Structural alignments show two NPA motifs gen

Ref: Fujiyoshi et al., Structure of Aquaporin Water Channel and NPA Motif, Nature 2002.

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Membrane Transportation

Which of the following molecules moves most efficiently through aquaporins?

Aquaporins represent a family of tetrameric channel proteins mediating extremely rapid yet selective water transport essential for osmoregulation, kidney concentration and brain water balance. Each monomer contains six transmembrane helices plus two half helices HB and HE each bearing conserved Asn-Pro-Ala motif that meet centrally forming dipoles. Water moves single file through an hourglass pore constricted to 2.8 angstrom at aromatic arginine filter where histidine, arginine and phenylalanine side chains create size barrier. Permeation rate exceeds one billion molecules per second per monom

Ref: Agre et al., Nobel Lecture 2003, Aquaporin Water Channels Structure - NPA Motifs and Proton Exclusion.

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