Crucial Role of the Double Bond Isomerism in the Steroid B-Ring on the Membrane Properties of Sterols. Grazing Incidence X-Ray Diffraction and Brewster Angle Microscopy Studies

Abstract

Three cholesterol precursors-desmosterol, zymosterol, and lanosterol-were comprehensively characterized in monolayers formed at the air/water interface. The studies were based on registration of the surface pressure (π)-area (A) isotherms complemented with in situ analysis performed with application of modern physicochemical techniques: grazing incidence X-ray diffraction (GIXD) and Brewster angle microscopy (BAM). In this approach we were interested in the correlation between molecular structures of the studied sterols found in the cholesterol biosynthetic pathway and their membrane properties. Our results revealed that only desmosterol behaves in Langmuir monolayers comparably to cholesterol, the molecules of which arrange in the monolayers into a hexagonal lattice, while the two remaining sterols possess extremely different properties. We found that molecules of both zymosterol and lanosterol are organized on the water surface in the two-dimensional oblique unit cells despite the fact that they are oriented perpendicular to the monolayer plane. The comparison of chemical structures of the investigated sterols leads to the conclusion that the only structural motive that can be responsible for such unusual behavior is the double bond in the B sterol ring, which is located in desmosterol in a different position from in the other two sterols. This issue, which was neglected in the scientific literature, seems to have crucial importance for sterol activity in biomembranes. We showed that this structural modification in sterol molecules is directly responsible for their adaptation to proper functioning in biomembranes.

A visible-light activated [2 + 2] cycloaddition reaction enables pinpointing carbon–carbon double bonds in lipids

“…Likewise, locations of ve other C]C bonds could be obtained. Therefore, the above evidence indicated that the detailed structure for one of the PC 38:6 isomers should be PC 16:0_22:6 (4,7,10,13,16,19).…”

“…The C]C bonds in positional isomers of unsaturated lipids endow them with different structures and functions in living organisms. 2,[11][12][13] For instance, lipids with cis-C]C in the fatty acyl chain were found to modulate plasma membrane domain registration/anti-registration. 14 Signicant correlations between the C]C positional isomer and the onset/progression of breast cancer were also observed.…”

【Original Contribution】Potential Interaction Behavior of Lanosterol and Unsaturated Phosphocholine in Monolayer Membrane

“…1). Cs -1 150 mN/m 19,30) . The elasticity values for each monolayer was calculated at surface pressure of 30 mN/m (Table 1) In bilayer studies 14) , Lan at 50 mol% in DOPC bilayer resulted in the dehydration.…”

“…Particularly, the double bond of B ring in sterols induces non planar structure, which decreases membrane packing 19) . Hence, Lan is classified in non-membrane active sterols 8) because Lan did not produce any co-existing solid or liquid phases in phospholipid bilayers 20) .…”

Plant Sterol Clustering Correlates with Membrane Microdomains as Revealed by Optical and Computational Microscopy

“…Brewster angle microscopy (BAM) is a powerful technique that provides a quantitative structural analysis of Langmuir monolayers. BAM imaging along with Langmuir techniques or X-ray reflectometry have also been widely used to study domain morphology and lateral phase separation in lipid monolayers and interfaces [ 12 , 13 , 14 , 15 , 16 ]. However, apart from cholesterol, the investigations on the other membrane sterols are not comprehensive in nature based on BAM approaches.…”