The Escherichia coli aquaporin-Z water channel (original) (raw)
Related papers
The aquaporin-Z water channel gene of Escherichia coli: Structure, organization and phylogeny
Biology of the Cell, 1997
Aquaporin water channel proteins are found throughout the plant and animal kingdoms, but the first prokaryotic water channel gene, aqpZ, was only recently identified in wild type Escherichiu coli (Calamita G et a2 (1995) J Biol Chem 270,29063-29066). Here we define the organization of aqpZ in E coli, produce the AqpZ protein and compare the AqpZ phylogeny to that of some known bacterial homologs.
Molecular Cloning and Characterization of AqpZ, a Water Channel from Escherichia coli
Journal of Biological Chemistry, 1995
The aquaporin family of molecular water channels is widely expressed throughout the plant and animal kingdoms. No bacterial aquaporins are known; however, sequence-related bacterial genes have been identified that encode glycerol facilitators (glpF). By homology cloning, a novel aquaporin-related DNA (aqpZ) was identified that contained no surface N-glycosylation consensus. The aqpZ RNA was not identified in mammalian mRNA by Northern analysis and exhibited bacterial codon usage preferences. Southern analysis failed to demonstrate aqpZ in mammalian genomic DNA, whereas a strongly reactive DNA was present in chromosomal DNA from Escherichia coli and other bacterial species and did not correspond to glpF. The aqpZ DNA isolated from E. coli contained a 693-base pair open reading frame encoding a polypeptide 28 -38% identical to known aquaporins. When compared with other aquaporins, aqpZ encodes a 10-residue insert preceding exofacial loop C, truncated NH 2 and COOH termini, and no cysteines at known mercury-sensitive sites. Expression of aqpZ cRNA conferred Xenopus oocytes with a 15-fold increase in osmotic water permeability, which was maximal after 5 days of expression, was not inhibited with HgCl 2 , exhibited a low activation energy (E a ؍ 3.8 kcal/mol), and failed to transport nonionic solutes such as urea and glycerol. In contrast, oocytes expressing glpF transported glycerol but exhibited limited osmotic water permeability. Phylogenetic comparison of aquaporins and homologs revealed a large separation between aqpZ and glpF, consistent with an ancient gene divergence.
J Mol Biol, 1999
Understanding the selectivity of aquaporin water channels will require structural and functional studies of wild-type and modified proteins; however, expression systems have not previously yielded aquaporins in the necessary milligram quantities. Here we report expression of a histidine-tagged form of Escherichia coli aquaporin-Z (AqpZ) in its homologous expression system. 10-His-AqpZ is solubilized and purified to near homogeneity in a single step with a final yield of ∼2.5 mg/l of culture. The histidine tag is removed by trypsin, yielding the native protein with the addition of three N-terminal residues, as confirmed by microsequencing. Sucrose gradient sedimentation analysis showed that the native, solubilized AqpZ protein is a trypsin-resistant tetramer. Unlike other known aquaporins, AqpZ tetramers are not readily dissociated by 1 % SDS at neutral pH. Hydrophilic reducing agents have a limited effect on the stability of the tetramer in 1 % SDS, whereas incubations for more than 24 hours, pH values below 5.6, or exposure to the hydrophobic reducing agent ethanedithiol cause dissociation into monomers. Cys20, but not Cys9, is necessary for the stability of the AqpZ tetramer in SDS. Upon reconstitution into proteoliposomes, AqpZ displays very high osmotic water permeability (pf ⩾ 10 × 10−14 cm3 s−1 subunit−1) and low Arrhenius activation energy (Ea = 3.7 kcal/mol), similar to mammalian aquaporin-1 (AQP1). No permeation by glycerol, urea or sorbitol was detected. Expression of native and modified AqpZ in milligram quantities has permitted biophysical characterization of this remarkably stable aquaporin tetramer, which is being utilized for high-resolution structural studies.
Regulation of the Escherichia coli water channel gene aqpZ
Proceedings of the National Academy of Sciences, 1998
Osmotic movement of water across bacterial cell membranes is postulated to be a homeostatic mechanism for maintaining cell turgor. The molecular water transporter remained elusive until discovery of the Escherichia coli water channel, AqpZ, however the regulation of the aqpZ gene expression and physiological function of the AqpZ protein are unknown. Northern analysis revealed a transcript of 0.7 kb, confirming the monocistronic nature of aqpZ. Regulatory studies performed with an aqpZ::lacZ low copy plasmid demonstrate enhanced expression during mid-logarithmic growth, and expression of the gene is dependent upon the extracellular osmolality, which increased in hypoosmotic environments but strongly reduced in hyperosmolar NaCl or KCl. While disruption of the chromosomal aqpZ is not lethal for E. coli, the colonies of the aqpZ knockout mutant are smaller than those of the parental wild-type strain. When cocultured with parental wild-type E. coli, the aqpZ knockout mutant exhibits markedly reduced colony formation when grown at 39°C. Similarly, the aqpZ knockout mutant also exhibits greatly reduced colony formation when grown at low osmolality, but this phenotype is reversed by overexpression of AqpZ protein. These results implicate AqpZ as a participant in the adaptive response of E. coli to hypoosmotic environments and indicate a requirement for AqpZ by rapidly growing cells.
The importance of aquaporin water channel protein structures
The EMBO Journal, 2000
The history of the water channel and recent structural and functional analyses of aquaporins are reviewed. These ubiquitous channels are important for bacteria, plants and animals, exhibit a pronounced sequence homology and share functional as well as structural similarities. Aquaporins allow water or small specific solutes to pass unhindered, but block the passage of ions to prevent dissipation of the transmembrane potential. Besides advances in structure determination, recent experiments suggest that many of these channels are regulated by pH variations, phosphorylation and binding of auxiliary proteins.
Cellular and Molecular Biology of the Aquaporin Water Channels
Annual Review of Biochemistry, 1999
The high water permeability characteristic of mammalian red cell membranes is now known to be caused by the protein AQP1. This channel freely permits movement of water across the cell membrane, but it is not permeated by other small, uncharged molecules or charged solutes. AQP1 is a tetramer with each subunit containing an aqueous pore likened to an hourglass formed by obversely arranged tandem repeats. Cryoelectron microscopy of reconstituted AQP1 membrane crystals has revealed the three-dimensional structure at 3-6 Å. AQP1 is distributed in apical and basolateral membranes of renal proximal tubules and descending thin limbs as well as capillary endothelia. Ten mammalian aquaporins have been identified in water-permeable tissues and fall into two groupings. Orthodox aquaporins are waterselective and include AQP2, a vasopressin-regulated water channel in renal collecting duct, in addition to AQP0, AQP4, and AQP5. Multifunctional aquaglyceroporins AQP3, AQP7, and AQP9 are permeated by water, glycerol, and some other solutes. Aquaporins are being defined in numerous other species including amphibia, insects, plants, and microbials. Members of the aquaporin family are implicated in numerous physiological processes as well as the pathophysiology of a wide range of clinical disorders.
Visualization of AqpZ-Mediated Water Permeability in Escherichia coli by Cryoelectron Microscopy
2000
Transport of water across the plasma membrane is a fundamental process occurring in all living organisms. In bacteria, osmotic movement of water across the cytoplasmic membrane is needed to maintain cellular turgor; however, the molecular mechanisms of this process are poorly defined. Involvement of aquaporin water channels in bacterial water permeability was suggested by the recent discovery of the aquaporin gene, aqpZ, in Escherichia coli. By employing cryoelectron microscopy to compare E. coli cells containing (AqpZ ؉ ) and lacking (AqpZ ؊ ) aquaporin, we show that the AqpZ water channel rapidly mediates large water fluxes in response to sudden changes in extracellular osmolarity. These findings (i) demonstrate for the first time functional expression of a prokaryotic water channel, (ii) evidence the bidirectional water channel feature of AqpZ, (iii) document a role for AqpZ in bacterial osmoregulation, and (iv) define a suitable model for studying the physiology of prokaryotic water transport.
Structure and Function of Aquaporins: the Membrane Water Channel Proteins
Biointerface Research in Applied Chemistry, 2021
Aquaporins are integral membrane proteins which are also known as water channel proteins. They aid quick transportation of water across membranes and are important in controlling cell volume and transcellular water passage. Aquaporins are present in organisms, and they vary from archaea and bacteria to plants and animals. They are also found in insects and yeast. Presently, 13 mammalian aquaporins (AQP0 to AQP12) have been cloned and identified in every tissue in the body. These aquaporins are alike in basic structure with monomers containing six transmembrane and two short helical segments that enclose cytoplasmic and extracellular vestibules linked by aqueous pore. They have distinctive structures that define their functions, mode of action, and even their various control methods. Phylogenetic analysis of aquaporin consists of aquaporins, glycerol facilitators, plasma membrane integral proteins of plants, tonoplast integral proteins of plants, nodules of plants, and AQP8s. Aquapor...
Aquaporins: A Multidisciplinary Perspective on The Water Channel Proteins
Acta Medica, 2020
Aquaporins are unique water channel proteins located at cell membranes that possess high water permeability and high solute rejection. Their primary function is to maintain the osmotic balance of the cells via regulating the water transport. However, their discovery had also provided the scientists to understand the pathophysiology of some diseases. In fact, aquaporins are shown to be strongly related to cancer by taking part in several tumor-related processes such as cell migration, cell proliferation and cell adhesion. Other than their functions in human body, recently, aquaporins have started to be used in engineering biomimetic membranes, for different applications such as desalination. This review investigates the properties and functions of the aquaporins in a multidisciplinary point of view and demonstrates the recent developments in aquaporin-based research.
The EMBO Journal
Aquaporins form a large family of membrane channels involved in osmoregulation. Electron crystallography has shown monomers to consist of six membrane spanning α-helices confirming sequence based predictions. Surface exposed loops are the least conserved regions, allowing differentiation of aquaporins. Atomic force microscopy was used to image the surface of aquaporin Z, the water channel of Escherichia coli. Recombinant protein with an N-terminal fragment including 10 histidines was isolated as a tetramer by Ni-affinity chromatography, and reconstituted into twodimensional crystals with p42 1 2 symmetry. Small crystalline areas with p4 symmetry were found as well. Imaging both crystal types before and after cleavage of the N-termini allowed the cytoplasmic surface to be identified; a drastic change of the cytoplasmic surface accompanied proteolytic cleavage, while the extracellular surface morphology did not change. Flexibility mapping and volume calculations identified the longest loop at the extracellular surface. This loop exhibited a reversible force-induced conformational change.