Membranes are vital components of biological systems, fulfilling a myriad of roles in the cell [1]. Despite their highly diverse composition, they are primarily comprised of zwitterionic and anionic lipids which, in some cases, makes them sensitive to changes in pH. In computational methods, the inherent complexity of these systems is often simplified via the use of model membranes normally composed of a single lipid type or, in some cases, of binary or ternary mixtures. While these approximations are generally adequate, there are particular instances where the pH, and consequently, the titration of lipid headgroups, plays a key role in membrane stability and function, meaning that the development of more realistic membrane models is extremely important.

Previously, we reported in simulations of a 25% PA/PC (phosphatidic acid/phosphatidylcholine) mixture a pH-dependent phase transition from gel to fluid [2]. In this work, we assembled binary mixtures of either phosphatidylglycerol (PG) or phosphatidylserine (PS) in phosphatidylcholine (PC) with different molar fractions (10%, 25%, 50% or 75% of PG or PS) and studied the effect of pH using the latest implementation of our constant-pH MD method with lipid titration (CpHMD-L) [2].

Acknowledgments

We acknowledge financial support from FCT through grant SFRH/BPD/110491/2015 and projects PTDC/QEQCOM/5904/2014, UID/MULTI/00612/2013 and UID/MULTI/04046/2013.

References

[1] Edidin, M., NRMCB, 4 (2003) 414.

[2] Santos, H.A.F., Vila-Viçosa, D., Teixeira, V.H., Baptista, A.M., Machuqueiro, M. JCTC, 11 (2015) 5973