Effects of gramicidin-A on the adsorption of phospholipids to the air–water interface

Biswas, Samares C.; Rananavare, Shankar B.; Hall, Stephen B.

doi:10.1016/j.bbamem.2005.09.006

Cited by 27 publications

(40 citation statements)

References 49 publications

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“…The components of surfactant vesicles insert into the interface collectively (16)(17)(18). As with fusion, several compounds affect adsorption according to how they alter curvature (19)(20)(21)(22)(23). These results suggest that surfactant proteins might accelerate adsorption by facilitating the formation of a negatively curved, rate-limiting intermediate ( Fig.…”

Section: Introductionmentioning

confidence: 88%

Hydrophobic Surfactant Proteins Strongly Induce Negative Curvature

Chavarha

Loney

Rananavare

et al. 2015

Biophysical Journal

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The hydrophobic surfactant proteins SP-B and SP-C greatly accelerate the adsorption of vesicles containing the surfactant lipids to form a film that lowers the surface tension of the air/water interface in the lungs. Pulmonary surfactant enters the interface by a process analogous to the fusion of two vesicles. As with fusion, several factors affect adsorption according to how they alter the curvature of lipid leaflets, suggesting that adsorption proceeds via a rate-limiting structure with negative curvature, in which the hydrophilic face of the phospholipid leaflets is concave. In the studies reported here, we tested whether the surfactant proteins might promote adsorption by inducing lipids to adopt a more negative curvature, closer to the configuration of the hypothetical intermediate. Our experiments used x-ray diffraction to determine how the proteins in their physiological ratio affect the radius of cylindrical monolayers in the negatively curved, inverse hexagonal phase. With binary mixtures of dioleoylphosphatidylethanolamine (DOPE) and dioleoylphosphatidylcholine (DOPC), the proteins produced a dose-related effect on curvature that depended on the phospholipid composition. With DOPE alone, the proteins produced no change. With an increasing mol fraction of DOPC, the response to the proteins increased, reaching a maximum 50% reduction in cylindrical radius at 5% (w/w) protein. This change represented a doubling of curvature at the outer cylindrical surface. The change in spontaneous curvature, defined at approximately the level of the glycerol group, would be greater. Analysis of the results in terms of a Langmuir model for binding to a surface suggests that the effect of the lipids is consistent with a change in the maximum binding capacity. Our findings show that surfactant proteins can promote negative curvature, and support the possibility that they facilitate adsorption by that mechanism.

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Section: Introductionmentioning

confidence: 88%

Hydrophobic Surfactant Proteins Strongly Induce Negative Curvature

Chavarha

Loney

Rananavare

et al. 2015

Biophysical Journal

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“…The proteins accelerate adsorption whether restricted to the vesicles or to preexisting films at the interface. 5, 6 These findings suggest that the proteins affect a rate-limiting structure that is accessible from both locations. An hourglass-shaped stalk extending between the adsorbing vesicles and the air/water interface 7, 8 (Fig.…”

Section: Introductionmentioning

confidence: 91%

Differential Effects of the Hydrophobic Surfactant Proteins on the Formation of Inverse Bicontinuous Cubic Phases

et al. 2012

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Prior studies have shown that the biological mixture of the two hydrophobic surfactant proteins, SP–B and SP–C, produces faster adsorption of the surfactant lipids to an air/water interface, and that they induce 1-palmitoyl-2-oleoyl phosphatidylethanolamine (POPE) to form inverse bicontinuous cubic phases. Previous studies have shown that SP–B has a much greater effect than SP–C on adsorption. If the two proteins induce faster adsorption and formation of the bicontinuous structures by similar mechanisms, then they should also have different abilities to form the cubic phases. To test this hypothesis, we measured small angle X-ray scattering on the individual proteins combined with POPE. SP–B replicated the dose-related ability of the combined proteins to induce the cubic phases at temperatures more than 25°C below the point at which POPE alone forms the curved inverse-hexagonal phase. With SP–C, diffraction from cubic structures was either absent or present at very low intensities only with larger amounts of protein. The correlation between the structural effects of inducing curved structures and the functional effects on the rate of adsorption fits with the model in which SP–B promotes adsorption by facilitating formation of an inversely curved, rate-limiting structure.

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“…In lipid mixtures without the surfactant proteins, factors that promote formation of the H II phase, including both lipids (Yu et al, 1984; Perkins et al, 1996; Biswas et al, 2007) and peptides (Biswas et al, 2005), accelerate adsorption. Although this observation suggests that adsorption of phospholipids, like the fusion of vesicles, proceeds via a structure with negative curvature, adsorption of these model systems and of pulmonary surfactant could proceed along different pathways.…”

Section: Adsorptionmentioning

confidence: 99%

The biophysical function of pulmonary surfactant

Rugonyi

Biswas

Hall

2008

Respiratory Physiology & Neurobiology

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153

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Pulmonary surfactant lowers surface tension in the lungs. Physiological studies indicate two key aspects of this function: that the surfactant film forms rapidly; and that when compressed by the shrinking alveolar area during exhalation, the film reduces surface tension to very low values. These observations suggest that surfactant vesicles adsorb quickly, and that during compression, the adsorbed film resists the tendency to collapse from the interface to form a three-dimensional bulk phase. Available evidence suggests that adsorption occurs by way of a rate-limiting structure that bridges the gap between the vesicle and the interface, and that the adsorbed film avoids collapse by undergoing a process of solidification. Current models, although incomplete, suggest mechanisms that would partially explain both rapid adsorption and resistance to collapse as well as how different constituents of pulmonary surfactant might affect its behavior.

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Effects of gramicidin-A on the adsorption of phospholipids to the air–water interface

Cited by 27 publications

References 49 publications

Hydrophobic Surfactant Proteins Strongly Induce Negative Curvature

Hydrophobic Surfactant Proteins Strongly Induce Negative Curvature

Differential Effects of the Hydrophobic Surfactant Proteins on the Formation of Inverse Bicontinuous Cubic Phases

The biophysical function of pulmonary surfactant

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