Delineation of the dynamic properties of individual lipid species in native and synthetic pulmonary surfactants

• The major lipids in CLSE exhibit lamellar properties at physiologic temperature, with phase separation of DPPC observed a lower temperatures.
• The dynamics of the major lipids in CLSE are unchanged by protein removal.
• The lipid properties of CLSE are closely matched by a synthetic PS lipid mixture.
• Addition of SP-B1 -25 to CLSE lipids specifically alters the phase properties of DPPC.
• DPPC dynamics induced by SP-B1 -25 in PS indicate the formation of a new lipid phase.

Pulmonary surfactant (PS) is characterized by a highly conserved lipid composition and the formation of unique multilamellar structures within the lung. An unusually high concentration of DPPC is a hallmark of PS and is critical to the formation of a high surface area, stable air/water interface; the unusual lipid polymorphisms observed in PS are dependent on surfactant proteins, particularly lung surfactant protein B (SP-B). The molecular mechanisms of lipid trafficking and assembly in PS remain largely uncharacterized. Using 2H and 31P NMR, we characterize the dynamics and polymorphisms of the major lipid species in native PS and synthetic lipid mixtures as a function of SP-B1 -25 addition. Our findings point to increased dynamics and a departure from a lamellar behavior for DPPC on addition of the peptide, consistent with our observations of DPPC phase separation in native surfactant. The monounsaturated lipids POPC, POPG and POPE remain in a lamellar phase and are less affected than DPPC by surfactant peptide addition. Additionally, we demonstrate that the properties of a native PS can be successfully mimicked by using a fully synthetic lipid mixture allowing the efficient evaluation of peptidomimetics under development for PS replacement therapies via NMR spectroscopy. The specificity of the dynamic changes in DPPC relative to POPC suggests the importance of tuning partitioning properties in successful peptidomimetic design. This article is part of a Special Issue entitled: NMR Spectroscopy for Atomistic Views of Biomembranes and Cell Surfaces. Guest Editors: Lynette Cegelski and David P. Weliky.

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