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Lung surfactant protein A (SP-A) interactions with model lung surfactant lipids and an SP-B fragment.

Sarker M, Jackman D, Booth V - Biochemistry (2011)

Bottom Line: We have also probed SP-A's interaction with Mini-B, a biologically active synthetic fragment of SP-B, in the presence of micelles.Despite variations in Mini-B's own interactions with micelles of different compositions, SP-A is found to interact with Mini-B in all micelle systems and perhaps to undergo a further structural rearrangement upon interacting with Mini-B.The degree of SP-A-Mini-B interaction appears to be dependent on the type of lipid headgroup and is likely mediated through the micelles, rather than direct binding.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics and Physical Oceanography, Memorial University of Newfoundland, St. John's, NL, Canada.

ABSTRACT
Surfactant protein A (SP-A) is the most abundant protein component of lung surfactant, a complex mixture of proteins and lipids. SP-A performs host defense activities and modulates the biophysical properties of surfactant in concerted action with surfactant protein B (SP-B). Current models of lung surfactant mechanism generally assume SP-A functions in its octadecameric form. However, one of the findings of this study is that when SP-A is bound to detergent and lipid micelles that mimic lung surfactant phospholipids, it exists predominantly as smaller oligomers, in sharp contrast to the much larger forms observed when alone in water. These investigations were carried out in sodium dodecyl sulfate (SDS), dodecylphosphocholine (DPC), lysomyristoylphosphatidylcholine (LMPC), lysomyristoylphosphatidylglycerol (LMPG), and mixed LMPC + LMPG micelles, using solution and diffusion nuclear magnetic resonance (NMR) spectroscopy. We have also probed SP-A's interaction with Mini-B, a biologically active synthetic fragment of SP-B, in the presence of micelles. Despite variations in Mini-B's own interactions with micelles of different compositions, SP-A is found to interact with Mini-B in all micelle systems and perhaps to undergo a further structural rearrangement upon interacting with Mini-B. The degree of SP-A-Mini-B interaction appears to be dependent on the type of lipid headgroup and is likely mediated through the micelles, rather than direct binding.

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Related in: MedlinePlus

2D 15N–1H HSQC spectra of Mini-B in different micelles in the absence (top panels) and presence (bottom panels) of SP-A. 0.2 mM Mini-B (A) and 0.1 mM Mini-B + 0.1 mM SP-A (F) in 40 mM SDS. 0.2 mM Mini-B (B) and 0.1 mM Mini-B + 0.1 mM SP-A (G) in 40 mM DPC. 0.25 mM Mini-B (C) and 0.125 mM Mini-B + 0.125 mM SP-A (H) in 50 mM LMPC. 0.25 mM Mini-B (D) and 0.125 mM Mini-B + 0.125 mM SP-A (I) in 50 mM LMPG. 0.25 mM Mini-B (E) and 0.125 mM Mini-B + 0.125 mM SP-A (J) in 42.5 mM LMPC + 7.5 mM LMPG. Spectra A–E were acquired using 160 scans, and spectra F–J were acquired using 320 scans.
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fig4: 2D 15N–1H HSQC spectra of Mini-B in different micelles in the absence (top panels) and presence (bottom panels) of SP-A. 0.2 mM Mini-B (A) and 0.1 mM Mini-B + 0.1 mM SP-A (F) in 40 mM SDS. 0.2 mM Mini-B (B) and 0.1 mM Mini-B + 0.1 mM SP-A (G) in 40 mM DPC. 0.25 mM Mini-B (C) and 0.125 mM Mini-B + 0.125 mM SP-A (H) in 50 mM LMPC. 0.25 mM Mini-B (D) and 0.125 mM Mini-B + 0.125 mM SP-A (I) in 50 mM LMPG. 0.25 mM Mini-B (E) and 0.125 mM Mini-B + 0.125 mM SP-A (J) in 42.5 mM LMPC + 7.5 mM LMPG. Spectra A–E were acquired using 160 scans, and spectra F–J were acquired using 320 scans.

Mentions: SP-A samples were prepared in aqueous solution (90% H2O + 10% D2O) containing 0.4 mM 2,2-dimethyl-2-silapentane-5-sulfonate (DSS), 0.2 mM NaN3, and 4.5 mM Hepes. SP-A–micelle samples were prepared by adding the required amounts of detergents/lipids to the aqueous sample. At least two samples were prepared for each micelle system with differing ratios of the protein to detergent/lipid. However, for each sample, the molar concentration of the detergent/lipid was kept at least 200 times higher than the monomeric concentration of SP-A. The exact protein and detergent/lipid concentrations of the samples are mentioned in the captions of Figures 1–4. For SDS and DPC samples, deuterated (98%) detergents, purchased from Cambridge Isotope Laboratories (Andover, MA), were used. For LMPC and LMPG samples, nondeuterated lipids, purchased from Avanti Polar Lipids (Alabaster, AL), were used as their deuterated versions were not commercially available. The samples were set to pH 6.9 using NaOH and HCl solutions. Mini-B samples were prepared separately, maintaining identical conditions to the SP-A samples. Finally, SP-A and Mini-B samples in each micelle system were mixed together at equal quantities (i.e., a protein monomer ratio of 1 to 1) to prepare the mixed protein samples.


Lung surfactant protein A (SP-A) interactions with model lung surfactant lipids and an SP-B fragment.

Sarker M, Jackman D, Booth V - Biochemistry (2011)

2D 15N–1H HSQC spectra of Mini-B in different micelles in the absence (top panels) and presence (bottom panels) of SP-A. 0.2 mM Mini-B (A) and 0.1 mM Mini-B + 0.1 mM SP-A (F) in 40 mM SDS. 0.2 mM Mini-B (B) and 0.1 mM Mini-B + 0.1 mM SP-A (G) in 40 mM DPC. 0.25 mM Mini-B (C) and 0.125 mM Mini-B + 0.125 mM SP-A (H) in 50 mM LMPC. 0.25 mM Mini-B (D) and 0.125 mM Mini-B + 0.125 mM SP-A (I) in 50 mM LMPG. 0.25 mM Mini-B (E) and 0.125 mM Mini-B + 0.125 mM SP-A (J) in 42.5 mM LMPC + 7.5 mM LMPG. Spectra A–E were acquired using 160 scans, and spectra F–J were acquired using 320 scans.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3104520&req=5

fig4: 2D 15N–1H HSQC spectra of Mini-B in different micelles in the absence (top panels) and presence (bottom panels) of SP-A. 0.2 mM Mini-B (A) and 0.1 mM Mini-B + 0.1 mM SP-A (F) in 40 mM SDS. 0.2 mM Mini-B (B) and 0.1 mM Mini-B + 0.1 mM SP-A (G) in 40 mM DPC. 0.25 mM Mini-B (C) and 0.125 mM Mini-B + 0.125 mM SP-A (H) in 50 mM LMPC. 0.25 mM Mini-B (D) and 0.125 mM Mini-B + 0.125 mM SP-A (I) in 50 mM LMPG. 0.25 mM Mini-B (E) and 0.125 mM Mini-B + 0.125 mM SP-A (J) in 42.5 mM LMPC + 7.5 mM LMPG. Spectra A–E were acquired using 160 scans, and spectra F–J were acquired using 320 scans.
Mentions: SP-A samples were prepared in aqueous solution (90% H2O + 10% D2O) containing 0.4 mM 2,2-dimethyl-2-silapentane-5-sulfonate (DSS), 0.2 mM NaN3, and 4.5 mM Hepes. SP-A–micelle samples were prepared by adding the required amounts of detergents/lipids to the aqueous sample. At least two samples were prepared for each micelle system with differing ratios of the protein to detergent/lipid. However, for each sample, the molar concentration of the detergent/lipid was kept at least 200 times higher than the monomeric concentration of SP-A. The exact protein and detergent/lipid concentrations of the samples are mentioned in the captions of Figures 1–4. For SDS and DPC samples, deuterated (98%) detergents, purchased from Cambridge Isotope Laboratories (Andover, MA), were used. For LMPC and LMPG samples, nondeuterated lipids, purchased from Avanti Polar Lipids (Alabaster, AL), were used as their deuterated versions were not commercially available. The samples were set to pH 6.9 using NaOH and HCl solutions. Mini-B samples were prepared separately, maintaining identical conditions to the SP-A samples. Finally, SP-A and Mini-B samples in each micelle system were mixed together at equal quantities (i.e., a protein monomer ratio of 1 to 1) to prepare the mixed protein samples.

Bottom Line: We have also probed SP-A's interaction with Mini-B, a biologically active synthetic fragment of SP-B, in the presence of micelles.Despite variations in Mini-B's own interactions with micelles of different compositions, SP-A is found to interact with Mini-B in all micelle systems and perhaps to undergo a further structural rearrangement upon interacting with Mini-B.The degree of SP-A-Mini-B interaction appears to be dependent on the type of lipid headgroup and is likely mediated through the micelles, rather than direct binding.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics and Physical Oceanography, Memorial University of Newfoundland, St. John's, NL, Canada.

ABSTRACT
Surfactant protein A (SP-A) is the most abundant protein component of lung surfactant, a complex mixture of proteins and lipids. SP-A performs host defense activities and modulates the biophysical properties of surfactant in concerted action with surfactant protein B (SP-B). Current models of lung surfactant mechanism generally assume SP-A functions in its octadecameric form. However, one of the findings of this study is that when SP-A is bound to detergent and lipid micelles that mimic lung surfactant phospholipids, it exists predominantly as smaller oligomers, in sharp contrast to the much larger forms observed when alone in water. These investigations were carried out in sodium dodecyl sulfate (SDS), dodecylphosphocholine (DPC), lysomyristoylphosphatidylcholine (LMPC), lysomyristoylphosphatidylglycerol (LMPG), and mixed LMPC + LMPG micelles, using solution and diffusion nuclear magnetic resonance (NMR) spectroscopy. We have also probed SP-A's interaction with Mini-B, a biologically active synthetic fragment of SP-B, in the presence of micelles. Despite variations in Mini-B's own interactions with micelles of different compositions, SP-A is found to interact with Mini-B in all micelle systems and perhaps to undergo a further structural rearrangement upon interacting with Mini-B. The degree of SP-A-Mini-B interaction appears to be dependent on the type of lipid headgroup and is likely mediated through the micelles, rather than direct binding.

Show MeSH
Related in: MedlinePlus