Methanol Accelerates DMPC Flip-Flop and Transfer: A SANS Study on Lipid Dynamics

Abstract

Methanol is a common solubilizing agent used to study transmembrane proteins/peptides in biological and synthetic membranes. Using small angle neutron scattering and a strategic contrast-matching scheme, we show that methanol has a major impact on lipid dynamics. Under increasing methanol concentrations, isotopically distinct 1,2-dimyristoyl-sn-glycero-3phosphocholine large unilamellar vesicle populations exhibit increased mixing. Specifically, 1,2-dimyristoyl-sn-glycero-3-phosphocholine transfer and flip-flop kinetics display linear and exponential rate enhancements, respectively. Ultimately, methanol is capable of influencing the structure-function relationship associated with bilayer composition (e.g., lipid asymmetry). The use of methanol as a carrier solvent, despite better simulating some biological conditions (e.g., antimicrobial attack), can help misconstrue lipid scrambling as the action of proteins or peptides, when in actuality it is a combination of solvent and biological agent. As bilayer compositional stability is crucial to cell survival and protein reconstitution, these results highlight the importance of methanol, and solvents in general, in biomembrane and proteolipid studies.

Transverse lipid organization dictates bending fluctuations in model plasma membranes

“…Taken together, a structural description of interleaflet coupling is insufficient in explaining the findings in this work. In general, lipid dynamics may be more sensitive to changes in composition and perhaps other system conditions than structural features, a conclusion in line with a previous finding where a dramatic change in lipid flip-flop and intervesic- ular exchange rates in the presence of methanol was observed before any structural deviations were detected by SANS, SAXS or DLS 45 .…”

Breakage of Hydrophobic Contacts Limits the Rate of Passive Lipid Exchange between Membranes

“…We note that lipid flip-flop, the process by which a lipid moves between leaflets of the same bilayer, 1,5 also has a rate measured under some experimental conditions that is similar to the exchange rate. 75,90 Unlike vesicle fusion, lipid flip-flop is accounted for in experimental determination of lipid exchange rates.…”

Numerical Estimation of Acetonitrile Adsorption into Simple Artificial Cell Membranes

“…Methanol, which is a small polar molecule, can enhance the flip‐flop of lipid bilayers [23] . However, the ellipsoidal shape of lipid vesicles did not change during observations in the presence of acetonitrile [17] .…”

“…Methanol, which is a small polar molecule, can enhance the flip-flop of lipid bilayers. [23] However, the ellipsoidal shape of lipid vesicles did not change during observations in the [7,8] Line 1 represents Equation 8 with Da < ffi ffi ffi 2 p : (b) Enlarged view of (a). Lines 2 and 3 represent Equations 9 and 10, respectively.…”