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The mobility of single-file water molecules is governed by the number of H-bonds they may form with channel-lining residues.

Horner A, Zocher F, Preiner J, Ollinger N, Siligan C, Akimov SA, Pohl P - Sci Adv (2015)

Bottom Line: We show that both the p f of those channels and the diffusion coefficient of the single-file waters within them are determined by the number N H of residues in the channel wall that may form a hydrogen bond with the single-file waters.The logarithmic dependence of water diffusivity on N H is in line with the multiplicity of binding options at higher N H densities.We obtained high-precision p f values by (i) having measured the abundance of the reconstituted aquaporins in the vesicular membrane via fluorescence correlation spectroscopy and via high-speed atomic force microscopy, and (ii) having acquired the vesicular water efflux from scattered light intensities via our new adaptation of the Rayleigh-Gans-Debye equation.

View Article: PubMed Central - HTML - PubMed

Affiliation: Johannes Kepler University Linz, Institute of Biophysics, Gruberstr. 40, 4020 Linz, Austria.

ABSTRACT

Channel geometry governs the unitary osmotic water channel permeability, p f, according to classical hydrodynamics. Yet, p f varies by several orders of magnitude for membrane channels with a constriction zone that is one water molecule in width and four to eight molecules in length. We show that both the p f of those channels and the diffusion coefficient of the single-file waters within them are determined by the number N H of residues in the channel wall that may form a hydrogen bond with the single-file waters. The logarithmic dependence of water diffusivity on N H is in line with the multiplicity of binding options at higher N H densities. We obtained high-precision p f values by (i) having measured the abundance of the reconstituted aquaporins in the vesicular membrane via fluorescence correlation spectroscopy and via high-speed atomic force microscopy, and (ii) having acquired the vesicular water efflux from scattered light intensities via our new adaptation of the Rayleigh-Gans-Debye equation.

No MeSH data available.


Related in: MedlinePlus

Number NH of pore-lining residues (in yellow circles) that may form hydrogen bonds (dotted lines) with single-file water moleculesThe 0.88-Å resolution structure of yeast AQP1 (33) [Protein Data Bank (PDB) #3Z0J] served as a template to find a model for the AQP1 (PDB #1J4N), AQPZ (PDB #1RC2), and GlpF (PDB #1FX8) structures via the PyMol’s “align” routine (34). The position of the water molecules (red spheres) is from the yeast AQP1 structure. The two water molecules below R206 have been added in the GlpF model to indicate that this region is wide enough to let the water molecules bypass each other within the pore.
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Figure 4: Number NH of pore-lining residues (in yellow circles) that may form hydrogen bonds (dotted lines) with single-file water moleculesThe 0.88-Å resolution structure of yeast AQP1 (33) [Protein Data Bank (PDB) #3Z0J] served as a template to find a model for the AQP1 (PDB #1J4N), AQPZ (PDB #1RC2), and GlpF (PDB #1FX8) structures via the PyMol’s “align” routine (34). The position of the water molecules (red spheres) is from the yeast AQP1 structure. The two water molecules below R206 have been added in the GlpF model to indicate that this region is wide enough to let the water molecules bypass each other within the pore.

Mentions: We took the 0.88-Å resolution structure of yeast AQP1 (33) as a template and used PyMol (34) to construct homology models for AQP1, AQPZ, and GlpF (fig. S8). We count NH = 12 possible hydrogen bonds between the single-file waters and pore-lining residues in the plot that shows the water-filled cavity (Fig. 4). The twofold lower pf of AQPZ may be caused by closings of AQPZ (35). To allow for the passage of the comparatively large glycerol molecules, the constriction site of GlpF is wider and shorter than that of the pure water channels AQP1 and AQPZ. In contrast to the glycerol-free crystal structure and its molecular dynamics simulation (16), more recent simulations found the length of the single-file region to be halved in GlpF (10, 11). In agreement with the more recent simulations, we find NH = 6 from the homology model (Fig. 4). Because the single-file region contains only a small number of binding places, it is not surprising that GlpF has the highest pf among the three aquaporins investigated.


The mobility of single-file water molecules is governed by the number of H-bonds they may form with channel-lining residues.

Horner A, Zocher F, Preiner J, Ollinger N, Siligan C, Akimov SA, Pohl P - Sci Adv (2015)

Number NH of pore-lining residues (in yellow circles) that may form hydrogen bonds (dotted lines) with single-file water moleculesThe 0.88-Å resolution structure of yeast AQP1 (33) [Protein Data Bank (PDB) #3Z0J] served as a template to find a model for the AQP1 (PDB #1J4N), AQPZ (PDB #1RC2), and GlpF (PDB #1FX8) structures via the PyMol’s “align” routine (34). The position of the water molecules (red spheres) is from the yeast AQP1 structure. The two water molecules below R206 have been added in the GlpF model to indicate that this region is wide enough to let the water molecules bypass each other within the pore.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4496530&req=5

Figure 4: Number NH of pore-lining residues (in yellow circles) that may form hydrogen bonds (dotted lines) with single-file water moleculesThe 0.88-Å resolution structure of yeast AQP1 (33) [Protein Data Bank (PDB) #3Z0J] served as a template to find a model for the AQP1 (PDB #1J4N), AQPZ (PDB #1RC2), and GlpF (PDB #1FX8) structures via the PyMol’s “align” routine (34). The position of the water molecules (red spheres) is from the yeast AQP1 structure. The two water molecules below R206 have been added in the GlpF model to indicate that this region is wide enough to let the water molecules bypass each other within the pore.
Mentions: We took the 0.88-Å resolution structure of yeast AQP1 (33) as a template and used PyMol (34) to construct homology models for AQP1, AQPZ, and GlpF (fig. S8). We count NH = 12 possible hydrogen bonds between the single-file waters and pore-lining residues in the plot that shows the water-filled cavity (Fig. 4). The twofold lower pf of AQPZ may be caused by closings of AQPZ (35). To allow for the passage of the comparatively large glycerol molecules, the constriction site of GlpF is wider and shorter than that of the pure water channels AQP1 and AQPZ. In contrast to the glycerol-free crystal structure and its molecular dynamics simulation (16), more recent simulations found the length of the single-file region to be halved in GlpF (10, 11). In agreement with the more recent simulations, we find NH = 6 from the homology model (Fig. 4). Because the single-file region contains only a small number of binding places, it is not surprising that GlpF has the highest pf among the three aquaporins investigated.

Bottom Line: We show that both the p f of those channels and the diffusion coefficient of the single-file waters within them are determined by the number N H of residues in the channel wall that may form a hydrogen bond with the single-file waters.The logarithmic dependence of water diffusivity on N H is in line with the multiplicity of binding options at higher N H densities.We obtained high-precision p f values by (i) having measured the abundance of the reconstituted aquaporins in the vesicular membrane via fluorescence correlation spectroscopy and via high-speed atomic force microscopy, and (ii) having acquired the vesicular water efflux from scattered light intensities via our new adaptation of the Rayleigh-Gans-Debye equation.

View Article: PubMed Central - HTML - PubMed

Affiliation: Johannes Kepler University Linz, Institute of Biophysics, Gruberstr. 40, 4020 Linz, Austria.

ABSTRACT

Channel geometry governs the unitary osmotic water channel permeability, p f, according to classical hydrodynamics. Yet, p f varies by several orders of magnitude for membrane channels with a constriction zone that is one water molecule in width and four to eight molecules in length. We show that both the p f of those channels and the diffusion coefficient of the single-file waters within them are determined by the number N H of residues in the channel wall that may form a hydrogen bond with the single-file waters. The logarithmic dependence of water diffusivity on N H is in line with the multiplicity of binding options at higher N H densities. We obtained high-precision p f values by (i) having measured the abundance of the reconstituted aquaporins in the vesicular membrane via fluorescence correlation spectroscopy and via high-speed atomic force microscopy, and (ii) having acquired the vesicular water efflux from scattered light intensities via our new adaptation of the Rayleigh-Gans-Debye equation.

No MeSH data available.


Related in: MedlinePlus