| Structural highlights
3nk5 is a 2 chain structure with sequence from Ecoli. Full crystallographic information is available from OCA. For a guided tour on the structure components use FirstGlance.
| | Ligands: | |
| Related: | 1rc2, 2o9f, 3nka, 3nkc |
| Gene: | aqpZ, b0875, bniP, JW0859 (ECOLI) |
| Resources: | FirstGlance, OCA, PDBe, RCSB, PDBsum, ProSAT |
Function
[AQPZ_ECOLI] Channel that permits osmotically driven movement of water in both directions. It is involved in the osmoregulation and in the maintenance of cell turgor during volume expansion in rapidly growing cells. It mediates rapid entry or exit of water in response to abrupt changes in osmolarity.[1] [2] [3]
Evolutionary Conservation
Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf.
Publication Abstract from PubMed
Aquaporins are transmembrane channels that facilitate the permeation of water and small, uncharged amphipathic molecules across cellular membranes. One distinct aquaporin subfamily contains pure water channels, whereas a second subfamily contains channels that conduct small alditols such as glycerol, in addition to water. Distinction between these substrates is central to aquaporin function, though the contributions of protein structural motifs required for selectivity are not yet fully characterized. To address this question, we sequentially engineered three signature amino acids of the glycerol-conducting subfamily into the Escherichia coli water channel aquaporin Z (AqpZ). Functional analysis of these mutant channels showed a decrease in water permeability but not the expected increase in glycerol conduction. Using X-ray crystallography, we determined the atomic resolution structures of the mutant channels. The structures revealed a channel surprisingly similar in size to the wild-type AqpZ pore. Comparison with measured rates of transport showed that, as the size of the selectivity filter region of the channel approaches that of water, channel hydrophilicity dominated water conduction energetics. In contrast, the major determinant of selectivity for larger amphipathic molecules such as glycerol was channel cross-section size. Finally, we find that, although the selectivity filter region is indeed central to substrate transport, other structural elements that do not directly interact with the substrates, such as the loop connecting helices M6 and M7, and the C loop between helices C4 and C5, play an essential role in facilitating selectivity.
Structural context shapes the aquaporin selectivity filter.,Savage DF, O'Connell JD 3rd, Miercke LJ, Finer-Moore J, Stroud RM Proc Natl Acad Sci U S A. 2010 Oct 5;107(40):17164-9. Epub 2010 Sep 20. PMID:20855585[4]
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
References
- ↑ Delamarche C, Thomas D, Rolland JP, Froger A, Gouranton J, Svelto M, Agre P, Calamita G. Visualization of AqpZ-mediated water permeability in Escherichia coli by cryoelectron microscopy. J Bacteriol. 1999 Jul;181(14):4193-7. PMID:10400575
- ↑ Borgnia MJ, Kozono D, Calamita G, Maloney PC, Agre P. Functional reconstitution and characterization of AqpZ, the E. coli water channel protein. J Mol Biol. 1999 Sep 3;291(5):1169-79. PMID:10518952 doi:http://dx.doi.org/S0022-2836(99)93032-2
- ↑ Pohl P, Saparov SM, Borgnia MJ, Agre P. Highly selective water channel activity measured by voltage clamp: analysis of planar lipid bilayers reconstituted with purified AqpZ. Proc Natl Acad Sci U S A. 2001 Aug 14;98(17):9624-9. Epub 2001 Aug 7. PMID:11493683 doi:http://dx.doi.org/10.1073/pnas.161299398
- ↑ Savage DF, O'Connell JD 3rd, Miercke LJ, Finer-Moore J, Stroud RM. Structural context shapes the aquaporin selectivity filter. Proc Natl Acad Sci U S A. 2010 Oct 5;107(40):17164-9. Epub 2010 Sep 20. PMID:20855585 doi:10.1073/pnas.1009864107
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