Non-linear van't Hoff behavior in pulmonary surfactant model membranes

Author(s)

Vieira, Ernanni D. ; Basso, Luis G. M. ; Costa-Filho, Antonio J.

• Document type: Journal article
• Source: BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES; v. 1859, n. 6, p. 1133-1143, JUN 2017.
• Web of Science Citations: 3

Abstract

Pulmonary surfactant exhibits phase coexistence over a wide range of surface pressure and temperature. Less is known about the effect of temperature on pulmonary surfactant models. Given the lack of studies on this issue, we used electron paramagnetic resonance (EPR) and nonlinear least-squares (NLLS) simulations to investigate the thermotropic phase behavior of the matrix that mimics the pulmonary surfactant lipid complex, i.e., the lipid mixture composed of dipalmitoyl phosphatidylcholine (DPPC), palmitoyl-oleoyl phosphatidylcholine (POPC) and palmitoyl-oleoyl phosphatidylglycerol (POPG). Irrespective of pH, the EPR spectra recorded from 5 degrees C to 25 degrees C in the DPPC/POPC/POPG (4:3:1) model membrane contain two spectral components corresponding to lipids in gel-like and fluid-like phases, indicating a coexistence of two domains in that range. The temperature dependence of the distribution of spin labels between the domains yielded nonlinear van't Hoff plots. The thermodynamic parameters evaluated were markedly different for DPPC and for the ternary DPPC/POPC/POPG (4:3:1) membranes and exhibited a dependence on chemical environment. While enthalpy and entropy changes for DPPC were always positive and presented a quadratic behavior with temperature, those of the ternary mixture were linearly dependent on temperature and changed from negative to positive values. Despite that, enthalpy-entropy compensation takes place in the two systems. The thermotropic process associated with the coexistence of the two domains is entropically-driven in DPPC and either entropically- or enthalpically-driven in the pulmonary surfactant membrane depending on the pH, ionic strength and temperature. The significance of these results to the structure and function of the pulmonary surfactant lipid matrix is discussed. (C) 2017 Elsevier B.V. All rights reserved. (AU)

• FAPESP's process: 10/17662-8 - Electron magnetic resonance in studies of structure, function and interactions of biologically-relevant molecules
• Grantee: Antonio José da Costa Filho
• Support Opportunities: Regular Research Grants
• FAPESP's process: 14/00206-0 - Structure and function of SARS-CoV spike glycoprotein fusion peptides
• Grantee: Luís Guilherme Mansor Basso
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• FAPESP's process: 15/18390-5 - Electron magnetic resonance in molecular biophysics: new and old looks to new and old problems
• Grantee: Antonio José da Costa Filho
• Support Opportunities: Regular Research Grants