N- and O-methylation of sphingomyelin markedly affects its membrane properties and interactions with cholesterol

Abstract

We have prepared palmitoyl sphingomyelin (PSM) analogs in which either the 2-NH was methylated to NMe, the 3-OH was methylated to OMe, or both were methylated simultaneously. The aim of the study was to determine how such modifications in the membrane interfacial region of the molecules affected interlipid interactions in bilayer membranes. Measuring DPH anisotropy in vesicle membranes prepared from the SM analogs, we observed that methylation decreased gel-phase stability and increased fluid phase disorder, when compared to PSM. Methylation of the 2-NH had the largest effect on gel-phase instability (T(m) was lowered by ~7°C). Atomistic molecular dynamics simulations showed that fluid phase bilayers with methylated SM analogs were more expanded but thinner compared to PSM bilayers. It was further revealed that 3-OH methylation dramatically attenuated hydrogen bonding also via the amide nitrogen, whereas 2-NH methylation did not similarly affect hydrogen bonding via the 3-OH. The interactions of sterols with the methylated SM analogs were markedly affected. 3-OH methylation almost completely eliminated the capacity of the SM analog to form sterol-enriched ordered domains, whereas the 2-NH methylated SM analog formed sterol-enriched domains but these were less thermostable (and thus less ordered) than the domains formed by PSM. Cholestatrienol affinity to bilayers containing methylated SM analogs was also markedly reduced as compared to its affinity for bilayers containing PSM. Molecular dynamics simulations revealed further that cholesterol's bilayer location was deeper in PSM bilayers as compared to the location in bilayers made from methylated SM analogs. This study shows that the interfacial properties of SMs are very important for interlipid interactions and the formation of laterally ordered domains in complex bilayers.

Investigation of interfacial behavior of glycyrrhizin with a lipid raft model via a Langmuir monolayer study

“…However, a comparison between ΔG exc values in the DOPC/CHOL system (−1800 J mol −1 at 35 mN m −1 ) and those in the PSM/CHOL system (−2300 J mol −1 at 35 mN m −1 ) suggests that CHOL interacts more strongly with PSM than with DOPC through hydrogen bonding. These results support the evidence that the amide nitrogen of sphingomyelin (SM) has a possibility to bind to the 3-OH group of CHOL [63,64] for their attractive interaction.…”

Enzymatic Oxidation of Cholesterol: Properties and Functional Effects of Cholestenone in Cell Membranes

“…Both bilayers were hydrated with approximately 30000 water molecules. The initial membrane structures were obtained from our previous study [39]. To parameterize the interactions in the systems, for lipid molecules we used the all-atom optimized potentials for liquid simulation (OPLS) force field [40], following our previous works [41], [42].…”

Cholesterol stimulates and ceramide inhibits Sticholysin II-induced pore formation in complex bilayer membranes

“…At certain bilayer concentrations, which depend on the co-lipid properties, cholesterol can induce the formation of a liquid-ordered phase together with certain phospholipids [12]. Interestingly, cholesterol has been shown to associate with SM in bilayers [13], and this interaction is in part stabilized by hydrogen-bonding among SMs and between SM and cholesterol [14,15]. It has been speculated that domain formation (ordered cholesterol-enriched domains in an otherwise disordered bilayer) could help StnII or EqtII to form pores, even if the membrane affinity of the toxin is not very high (i.e., in the absence of SM) [5,9].…”