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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

The osmotic shrinkage of proteoliposomes(A) Representative stopped-flow raw data (spline lines) for AQPZ and the fit (dashed lines) according to Eq. 4. Equal volumes of vesicle suspension and hyperosmotic solution (300 mM sucrose) were mixed (5°C, same buffer as in Fig. 1). The number of reconstituted AQP monomers per proteoliposome is indicated. (B) Pf of reconstituted vesicles was calculated as shown in (A) for at least three independently purified and reconstituted batches for each protein and plotted as a function of the channel number per proteoliposome.
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Figure 2: The osmotic shrinkage of proteoliposomes(A) Representative stopped-flow raw data (spline lines) for AQPZ and the fit (dashed lines) according to Eq. 4. Equal volumes of vesicle suspension and hyperosmotic solution (300 mM sucrose) were mixed (5°C, same buffer as in Fig. 1). The number of reconstituted AQP monomers per proteoliposome is indicated. (B) Pf of reconstituted vesicles was calculated as shown in (A) for at least three independently purified and reconstituted batches for each protein and plotted as a function of the channel number per proteoliposome.

Mentions: Subsequently, we subjected the reconstituted vesicles to osmotic stress. V was determined by the vesicular water permeability Pf = Pf,l + Pf,c, which reflects the permeabilities Pf,c and Pf,l of all channels and the lipid bilayer, respectively:(3)V(t)=V0c0ic0i+cs{1+L(csci0exp(csc0i−APfVw(c0i+cs)2V0c0it))}where Vw, V0, A, , cs, and L are the molar volume of water, vesicle volume at time zero, surface area of the vesicle, the initial osmolyte concentration inside the vesicles, the incremental osmolyte concentration in the external solution due to sucrose addition, and the Lambert function L(x)eL(x) = x, respectively. V(t) is experimentally accessible by measuring I(t). To derive the corresponding expression, we exploited the Rayleigh-Gans-Debye relation (see the Supplementary Materials). We then substituted the dependence of the scattered light intensity on V for its Taylor series (figs. S1 and S2) and took into account the fraction α of bare vesicles, which does not contain any protein:(4)I(t)=a+b[αVbare(t)+(1−α)VAQP(t)]+d[αVbare(t)+(1−α)VAQP(t)]2where VAQP(t) and Vbare(t) are the volumes of proteoliposomes and bare vesicles, respectively. The parameter a is calculated as follows: , where . The fitting parameters b and d can be found analytically (see the Supplementary Materials) so that Pf may remain as the sole fitting parameter. However, this rather laborious procedure returned the same Pf value as the simpler fitting approach, which simultaneously determined b, d, and Pf for all test cases. When fitting Eq. 4 to the stopped-flow data (Fig. 2A), we fixed Pf,l to its value in pure lipid vesicles.


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)

The osmotic shrinkage of proteoliposomes(A) Representative stopped-flow raw data (spline lines) for AQPZ and the fit (dashed lines) according to Eq. 4. Equal volumes of vesicle suspension and hyperosmotic solution (300 mM sucrose) were mixed (5°C, same buffer as in Fig. 1). The number of reconstituted AQP monomers per proteoliposome is indicated. (B) Pf of reconstituted vesicles was calculated as shown in (A) for at least three independently purified and reconstituted batches for each protein and plotted as a function of the channel number per proteoliposome.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 2: The osmotic shrinkage of proteoliposomes(A) Representative stopped-flow raw data (spline lines) for AQPZ and the fit (dashed lines) according to Eq. 4. Equal volumes of vesicle suspension and hyperosmotic solution (300 mM sucrose) were mixed (5°C, same buffer as in Fig. 1). The number of reconstituted AQP monomers per proteoliposome is indicated. (B) Pf of reconstituted vesicles was calculated as shown in (A) for at least three independently purified and reconstituted batches for each protein and plotted as a function of the channel number per proteoliposome.
Mentions: Subsequently, we subjected the reconstituted vesicles to osmotic stress. V was determined by the vesicular water permeability Pf = Pf,l + Pf,c, which reflects the permeabilities Pf,c and Pf,l of all channels and the lipid bilayer, respectively:(3)V(t)=V0c0ic0i+cs{1+L(csci0exp(csc0i−APfVw(c0i+cs)2V0c0it))}where Vw, V0, A, , cs, and L are the molar volume of water, vesicle volume at time zero, surface area of the vesicle, the initial osmolyte concentration inside the vesicles, the incremental osmolyte concentration in the external solution due to sucrose addition, and the Lambert function L(x)eL(x) = x, respectively. V(t) is experimentally accessible by measuring I(t). To derive the corresponding expression, we exploited the Rayleigh-Gans-Debye relation (see the Supplementary Materials). We then substituted the dependence of the scattered light intensity on V for its Taylor series (figs. S1 and S2) and took into account the fraction α of bare vesicles, which does not contain any protein:(4)I(t)=a+b[αVbare(t)+(1−α)VAQP(t)]+d[αVbare(t)+(1−α)VAQP(t)]2where VAQP(t) and Vbare(t) are the volumes of proteoliposomes and bare vesicles, respectively. The parameter a is calculated as follows: , where . The fitting parameters b and d can be found analytically (see the Supplementary Materials) so that Pf may remain as the sole fitting parameter. However, this rather laborious procedure returned the same Pf value as the simpler fitting approach, which simultaneously determined b, d, and Pf for all test cases. When fitting Eq. 4 to the stopped-flow data (Fig. 2A), we fixed Pf,l to its value in pure lipid vesicles.

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