PDBsum entry 3nk5

Transport protein

PDB id: 3nk5

Contents

Protein chains

229 a.a. *

Ligands

BOG ×4

Waters ×136

* Residue conservation analysis

PDB id:

3nk5

Name:

Transport protein

Title:

Crystal structure of aqpz mutant f43w

Structure:

Aquaporin z. Chain: a, b. Fragment: chains a and b. Synonym: bacterial nodulin-like intrinsic protein. Engineered: yes. Mutation: yes

Source:

Escherichia coli. Organism_taxid: 83333. Strain: k12. Gene: aqpz, b0875, bnip, jw0859. Expressed in: escherichia coli. Expression_system_taxid: 562

Resolution:

2.40Å R-factor: 0.183 R-free: 0.220

Authors:

D.F.Savage,J.D.O'Connell,R.M.Stroud,J.S.Finer-Moore

Key ref:

D.F.Savage et al. (2010). Structural context shapes the aquaporin selectivity filter. Proc Natl Acad Sci U S A, 107, 17164-17169. PubMed id: 20855585

Date:

18-Jun-10 Release date: 11-Aug-10

Protein chains

P60844  (AQPZ_ECOLI) -  Aquaporin Z from Escherichia coli (strain K12)

Seq: 231 a.a.

Struc: 229 a.a.*

* PDB and UniProt seqs differ at 2 residue positions (black crosses)

Enzyme reactions

• Enzyme class: E.C.?

Proc Natl Acad Sci U S A 107:17164-17169 (2010)

PubMed id: 20855585

Structural context shapes the aquaporin selectivity filter.

D.F.Savage, J.D.O'Connell, L.J.Miercke, J.Finer-Moore, R.M.Stroud.

ABSTRACT

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.