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Architecture and selectivity in aquaporins: 2.5 a X-ray structure of aquaporin Z.

Savage DF, Egea PF, Robles-Colmenares Y, O'Connell JD, Stroud RM - PLoS Biol. (2003)

Bottom Line: The 2.5 A resolution structure of AqpZ suggests aquaporin selectivity results both from a steric mechanism due to pore size and from specific amino acid substitutions that regulate the preference for a hydrophobic or hydrophilic substrate.This structure provides direct evidence on the molecular mechanisms of specificity between water and glycerol in this family of channels from a single species.It is to our knowledge the first atomic resolution structure of a recombinant aquaporin and so provides a platform for combined genetic, mutational, functional, and structural determinations of the mechanisms of aquaporins and, more generally, the assembly of multimeric membrane proteins.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry and Biophysics, University of California School of Medicine, San Francisco, California, USA.

ABSTRACT
Aquaporins are a family of water and small molecule channels found in organisms ranging from bacteria to animals. One of these channels, the E. coli protein aquaporin Z (AqpZ), has been shown to selectively conduct only water at high rates. We have expressed, purified, crystallized, and solved the X-ray structure of AqpZ. The 2.5 A resolution structure of AqpZ suggests aquaporin selectivity results both from a steric mechanism due to pore size and from specific amino acid substitutions that regulate the preference for a hydrophobic or hydrophilic substrate. This structure provides direct evidence on the molecular mechanisms of specificity between water and glycerol in this family of channels from a single species. It is to our knowledge the first atomic resolution structure of a recombinant aquaporin and so provides a platform for combined genetic, mutational, functional, and structural determinations of the mechanisms of aquaporins and, more generally, the assembly of multimeric membrane proteins.

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Related in: MedlinePlus

Channel Constriction in Aquaporins(A) A view of the aquaporin selectivity filter from the periplasmic side. Experimental electron density (2Fobs – Fcalc ) is contoured at 1.1 σ.(B) Secondary constriction at the NPA motif due to F145 and L15. The drawn water is HOH1032, hydrogen-bonded to the NPA motif asparagines.(C) Pore diameters for the aquaporin X-ray structures, calculated with HOLE2. The AqpZ monomers (protomers) A and B refer to the crystallographically distinct monomers in the unit cell.
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pbio.0000072-g002: Channel Constriction in Aquaporins(A) A view of the aquaporin selectivity filter from the periplasmic side. Experimental electron density (2Fobs – Fcalc ) is contoured at 1.1 σ.(B) Secondary constriction at the NPA motif due to F145 and L15. The drawn water is HOH1032, hydrogen-bonded to the NPA motif asparagines.(C) Pore diameters for the aquaporin X-ray structures, calculated with HOLE2. The AqpZ monomers (protomers) A and B refer to the crystallographically distinct monomers in the unit cell.

Mentions: The channel contains two highly conserved regions, the selectivity filter and the NPA region. Located approximately 7 Å inside the periplasmic vestibule, the selectivity filter is the narrowest point (diameter of approximately 2 Å) in the entire channel (Figure 2). It is formed by the sidechains of F43(48), H174(191), and R189(206) and the carbonyl of T183(200). The trio of H174(191), T183(200), and R189(206) create a hydrophilic triangle opposite the hydrophobic F200.


Architecture and selectivity in aquaporins: 2.5 a X-ray structure of aquaporin Z.

Savage DF, Egea PF, Robles-Colmenares Y, O'Connell JD, Stroud RM - PLoS Biol. (2003)

Channel Constriction in Aquaporins(A) A view of the aquaporin selectivity filter from the periplasmic side. Experimental electron density (2Fobs – Fcalc ) is contoured at 1.1 σ.(B) Secondary constriction at the NPA motif due to F145 and L15. The drawn water is HOH1032, hydrogen-bonded to the NPA motif asparagines.(C) Pore diameters for the aquaporin X-ray structures, calculated with HOLE2. The AqpZ monomers (protomers) A and B refer to the crystallographically distinct monomers in the unit cell.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC300682&req=5

pbio.0000072-g002: Channel Constriction in Aquaporins(A) A view of the aquaporin selectivity filter from the periplasmic side. Experimental electron density (2Fobs – Fcalc ) is contoured at 1.1 σ.(B) Secondary constriction at the NPA motif due to F145 and L15. The drawn water is HOH1032, hydrogen-bonded to the NPA motif asparagines.(C) Pore diameters for the aquaporin X-ray structures, calculated with HOLE2. The AqpZ monomers (protomers) A and B refer to the crystallographically distinct monomers in the unit cell.
Mentions: The channel contains two highly conserved regions, the selectivity filter and the NPA region. Located approximately 7 Å inside the periplasmic vestibule, the selectivity filter is the narrowest point (diameter of approximately 2 Å) in the entire channel (Figure 2). It is formed by the sidechains of F43(48), H174(191), and R189(206) and the carbonyl of T183(200). The trio of H174(191), T183(200), and R189(206) create a hydrophilic triangle opposite the hydrophobic F200.

Bottom Line: The 2.5 A resolution structure of AqpZ suggests aquaporin selectivity results both from a steric mechanism due to pore size and from specific amino acid substitutions that regulate the preference for a hydrophobic or hydrophilic substrate.This structure provides direct evidence on the molecular mechanisms of specificity between water and glycerol in this family of channels from a single species.It is to our knowledge the first atomic resolution structure of a recombinant aquaporin and so provides a platform for combined genetic, mutational, functional, and structural determinations of the mechanisms of aquaporins and, more generally, the assembly of multimeric membrane proteins.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry and Biophysics, University of California School of Medicine, San Francisco, California, USA.

ABSTRACT
Aquaporins are a family of water and small molecule channels found in organisms ranging from bacteria to animals. One of these channels, the E. coli protein aquaporin Z (AqpZ), has been shown to selectively conduct only water at high rates. We have expressed, purified, crystallized, and solved the X-ray structure of AqpZ. The 2.5 A resolution structure of AqpZ suggests aquaporin selectivity results both from a steric mechanism due to pore size and from specific amino acid substitutions that regulate the preference for a hydrophobic or hydrophilic substrate. This structure provides direct evidence on the molecular mechanisms of specificity between water and glycerol in this family of channels from a single species. It is to our knowledge the first atomic resolution structure of a recombinant aquaporin and so provides a platform for combined genetic, mutational, functional, and structural determinations of the mechanisms of aquaporins and, more generally, the assembly of multimeric membrane proteins.

Show MeSH
Related in: MedlinePlus