Limits...
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
Oligomerization of AqpZ(A) Protomer–protomer interface. The interface is composed of helices M1 and M2 from one protomer (yellow) and M5 and M6 from a second protomer (blue). The helices participate in knobs into holes packing, and the interface is extensive (3,340 Δ2) owing to the large number of aromatic residues.(B) Abstruse electron density along the 4-fold axis (colored in green). Two protomers are display in surface rendering. The experimental electron density (2Fobs – Fcalc) is contoured at 1.1 σ.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC300682&req=5

pbio.0000072-g005: Oligomerization of AqpZ(A) Protomer–protomer interface. The interface is composed of helices M1 and M2 from one protomer (yellow) and M5 and M6 from a second protomer (blue). The helices participate in knobs into holes packing, and the interface is extensive (3,340 Δ2) owing to the large number of aromatic residues.(B) Abstruse electron density along the 4-fold axis (colored in green). Two protomers are display in surface rendering. The experimental electron density (2Fobs – Fcalc) is contoured at 1.1 σ.

Mentions: While it is clear the monomer is the functional unit, the existence of aquaporin tetramers in nature reinforces the importance of oligomerization. Fundamentally, tetramerization is driven by the energetically favorable assembly of four protomers. The protomer–protomer interface is large, tightly packed, and formed by helices M1 and M2 of one protomer and the quasi-2-fold related M5 and M6 of the neighboring protomer (Figure 5A). This interface is therefore repeated four times. In AqpZ, the interface is 3,340 Å2, in large part owing to the presence of 11 aromatic residues. The GlpF and AQP1 interfaces are 3,060 Å2 and 3,180 Å2, respectively, with five and three aromatic residues, respectively. Strikingly, the interface surface area correlates positively with biochemical stability; GlpF tends to aggregate in solution, AQP1 is well-behaved, and AqpZ is a stable tetramer in even mild denaturing conditions In this protomer–protomer interface, helices M2 and M6 form the tetramer pore.


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)

Oligomerization of AqpZ(A) Protomer–protomer interface. The interface is composed of helices M1 and M2 from one protomer (yellow) and M5 and M6 from a second protomer (blue). The helices participate in knobs into holes packing, and the interface is extensive (3,340 Δ2) owing to the large number of aromatic residues.(B) Abstruse electron density along the 4-fold axis (colored in green). Two protomers are display in surface rendering. The experimental electron density (2Fobs – Fcalc) is contoured at 1.1 σ.
© Copyright Policy
Related In: Results  -  Collection

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

pbio.0000072-g005: Oligomerization of AqpZ(A) Protomer–protomer interface. The interface is composed of helices M1 and M2 from one protomer (yellow) and M5 and M6 from a second protomer (blue). The helices participate in knobs into holes packing, and the interface is extensive (3,340 Δ2) owing to the large number of aromatic residues.(B) Abstruse electron density along the 4-fold axis (colored in green). Two protomers are display in surface rendering. The experimental electron density (2Fobs – Fcalc) is contoured at 1.1 σ.
Mentions: While it is clear the monomer is the functional unit, the existence of aquaporin tetramers in nature reinforces the importance of oligomerization. Fundamentally, tetramerization is driven by the energetically favorable assembly of four protomers. The protomer–protomer interface is large, tightly packed, and formed by helices M1 and M2 of one protomer and the quasi-2-fold related M5 and M6 of the neighboring protomer (Figure 5A). This interface is therefore repeated four times. In AqpZ, the interface is 3,340 Å2, in large part owing to the presence of 11 aromatic residues. The GlpF and AQP1 interfaces are 3,060 Å2 and 3,180 Å2, respectively, with five and three aromatic residues, respectively. Strikingly, the interface surface area correlates positively with biochemical stability; GlpF tends to aggregate in solution, AQP1 is well-behaved, and AqpZ is a stable tetramer in even mild denaturing conditions In this protomer–protomer interface, helices M2 and M6 form the tetramer pore.

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