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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.

Show MeSH
Water at the NPA RegionN63 and N186 donate hydrogen bonds to the central water by projecting their NH2 moieties into the pore. This conformation is aided by a hydrogen bond from the adjacent carbonyls of V185 and F62, respectively. Experimental electron density (2Fobs – Fcalc) is contoured at 0.7 σ.
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pbio.0000072-g004: Water at the NPA RegionN63 and N186 donate hydrogen bonds to the central water by projecting their NH2 moieties into the pore. This conformation is aided by a hydrogen bond from the adjacent carbonyls of V185 and F62, respectively. Experimental electron density (2Fobs – Fcalc) is contoured at 0.7 σ.

Mentions: Five waters are unambiguously located in the channel (Figure 4). The water is arranged in single file, with hydrogen bonding as donors to the projecting carbonyls from AqpZ and as donors to neighboring waters. From the periplasmic side to the cytoplasmic side, there are waters located adjacent to the carbonyls of T183(200) (OO distance of 3.0 Å), S184(201) (3.2 Å), H61(66) (3.0 Å), and G60(65) (3.4 Å). The waters are at appropriate (less than 3.2 Å) distances from each other for hydrogen bonding. No electron density was observed adjacent to the carbonyls of G59(64) or V185(202).


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)

Water at the NPA RegionN63 and N186 donate hydrogen bonds to the central water by projecting their NH2 moieties into the pore. This conformation is aided by a hydrogen bond from the adjacent carbonyls of V185 and F62, respectively. Experimental electron density (2Fobs – Fcalc) is contoured at 0.7 σ.
© Copyright Policy
Related In: Results  -  Collection

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

pbio.0000072-g004: Water at the NPA RegionN63 and N186 donate hydrogen bonds to the central water by projecting their NH2 moieties into the pore. This conformation is aided by a hydrogen bond from the adjacent carbonyls of V185 and F62, respectively. Experimental electron density (2Fobs – Fcalc) is contoured at 0.7 σ.
Mentions: Five waters are unambiguously located in the channel (Figure 4). The water is arranged in single file, with hydrogen bonding as donors to the projecting carbonyls from AqpZ and as donors to neighboring waters. From the periplasmic side to the cytoplasmic side, there are waters located adjacent to the carbonyls of T183(200) (OO distance of 3.0 Å), S184(201) (3.2 Å), H61(66) (3.0 Å), and G60(65) (3.4 Å). The waters are at appropriate (less than 3.2 Å) distances from each other for hydrogen bonding. No electron density was observed adjacent to the carbonyls of G59(64) or V185(202).

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