TY - JOUR
T1 - Suppression of Lα/Lβ Phase Coexistence in the Lipids of Pulmonary Surfactant
AU - Fritz, Jonathan R.
AU - Loney, Ryan W.
AU - Hall, Stephen B.
AU - Tristram-Nagle, Stephanie
N1 - Funding Information:
These studies were supported by the National Institutes of Health ( HL060914 , HL130130 , and HL136734 ). The Cornell High Energy Synchrotron Source was supported by the National Science Foundation under award number DMR-1332208 .
Funding Information:
The authors thank Yasmene Elhady, Diamond Moody, Akari Kumagai, Megan Roche, John Nagle, and Horia Petrache for help in collecting data at CHESS, and John Nagle for helpful discussions. These studies were supported by the National Institutes of Health (HL060914, HL130130, and HL136734). The Cornell High Energy Synchrotron Source was supported by the National Science Foundation under award number DMR-1332208.
Publisher Copyright:
© 2020 Biophysical Society
PY - 2021/1/19
Y1 - 2021/1/19
N2 - To determine how different constituents of pulmonary surfactant affect its phase behavior, we measured wide-angle x-ray scattering (WAXS) from oriented bilayers. Samples contained the nonpolar and phospholipids (N&PL) obtained from calf lung surfactant extract (CLSE), which also contains the hydrophobic surfactant proteins SP-B and SP-C. Mixtures with different ratios of N&PL and CLSE provided the same set of lipids with different amounts of the proteins. At 37°C, N&PL by itself forms coexisting Lα and Lβ phases. In the Lβ structure, the acyl chains of the phospholipids occupy an ordered array that has melted by 40°C. This behavior suggests that the Lβ composition is dominated by dipalmitoyl phosphatidylcholine (DPPC), which is the most prevalent component of CLSE. The Lβ chains, however, lack the tilt of the Lβ′ phase formed by pure DPPC. At 40°C, WAXS also detects an additional diffracted intensity, the location of which suggests a correlation among the phospholipid headgroups. The mixed samples of N&PL with CLSE show that increasing amounts of the proteins disrupt both the Lβ phase and the headgroup correlation. With physiological levels of the proteins in CLSE, both types of order are absent. These results with bilayers at physiological temperatures indicate that the hydrophobic surfactant proteins disrupt the ordered structures that have long been considered essential for the ability of pulmonary surfactant to sustain low surface tensions. They agree with prior fluorescence micrographic results from monomolecular films of CLSE, suggesting that at physiological temperatures, any ordered phase is likely to be absent or occupy a minimal interfacial area.
AB - To determine how different constituents of pulmonary surfactant affect its phase behavior, we measured wide-angle x-ray scattering (WAXS) from oriented bilayers. Samples contained the nonpolar and phospholipids (N&PL) obtained from calf lung surfactant extract (CLSE), which also contains the hydrophobic surfactant proteins SP-B and SP-C. Mixtures with different ratios of N&PL and CLSE provided the same set of lipids with different amounts of the proteins. At 37°C, N&PL by itself forms coexisting Lα and Lβ phases. In the Lβ structure, the acyl chains of the phospholipids occupy an ordered array that has melted by 40°C. This behavior suggests that the Lβ composition is dominated by dipalmitoyl phosphatidylcholine (DPPC), which is the most prevalent component of CLSE. The Lβ chains, however, lack the tilt of the Lβ′ phase formed by pure DPPC. At 40°C, WAXS also detects an additional diffracted intensity, the location of which suggests a correlation among the phospholipid headgroups. The mixed samples of N&PL with CLSE show that increasing amounts of the proteins disrupt both the Lβ phase and the headgroup correlation. With physiological levels of the proteins in CLSE, both types of order are absent. These results with bilayers at physiological temperatures indicate that the hydrophobic surfactant proteins disrupt the ordered structures that have long been considered essential for the ability of pulmonary surfactant to sustain low surface tensions. They agree with prior fluorescence micrographic results from monomolecular films of CLSE, suggesting that at physiological temperatures, any ordered phase is likely to be absent or occupy a minimal interfacial area.
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U2 - 10.1016/j.bpj.2020.12.008
DO - 10.1016/j.bpj.2020.12.008
M3 - Article
C2 - 33347885
AN - SCOPUS:85099116808
VL - 120
SP - 243
EP - 253
JO - Biophysical Journal
JF - Biophysical Journal
SN - 0006-3495
IS - 2
ER -