Lipid bilayers form topologically distinct phases depending on their composition, which regulate biological functions and define material properties. Cholesterol profoundly influences the fluid-to-gel phase transition in model phospholipid bilayers; however, its impact on the pre-transition ripple phase remains less defined and debated. Here we employed extensive all-atom simulations of pure dipalmitoylphosphatidylcholine (DPPC) and DPPC–cholesterol bilayers (with 15–30 mol% of cholesterol) at 30°C to investigate the rippling characteristics and cholesterol’s effect on their stability and organization in a concentration-dependent manner. Our results delineate the spontaneous formation of an asymmetric ripple pattern in the DPPC bilayer, having a periodic array of gel-like “major” and fluid-like “minor” arms. While the major arm is thick and ordered, and the minor arm is thinner and disordered with significant acyl chain splay and interdigitation, resulting in localized loss of bilayer structure and corrugated surface. Incorporation of cholesterol removes interdigitation and reduces the proportion of highly disordered lipids due to the ordering effect while also impeding acyl chain crystallization. At 15 mol%, cholesterol shows greater tendency to accumulate into relatively disordered domains that coexist with cholesterol-poor ordered domains. Thus, the peristaltic asymmetry of ripple pattern in absence of cholesterol transforms into symmetric ripple keeping the bilayer architecture intact. With increasing cholesterol concentration between 20 and 25 mol%, ripple periodicity causing bilayer undulation decreases gradually and at 30 mol% the bilayer turns into lamellar structure with homogeneous liquid-ordered phase and uniform cholesterol distribution. The present work comprehensively shows the effects of varying cholesterol concentrations on ripple nature and architecture of DPPC bilayer, and provides detailed atomistic insights into how cholesterol modulates the lipid organizations of different domains, acyl chain conformations, and lipid–lipid interactions driving to such transformation, adding to bridge the current gap in understanding cholesterol’s role in ripple phase regulation. Graphical abstract We characterized the ripple configuration of DPPC bilayer, which consists of a gel like major domain and also fluid like minor domain with interdigitation between leaflets and highly melted fatty acid chains. With addition of cholesterol, on concentration dependent manner, the ripple pattern of DPPC disrupts and with gradual addition of cholesterol the bilayer transforms into liquid-ordered phase.

Cholesterol modulation of the ripple phase in DPPC bilayer

期刊论文
发表日期：

2026年2月26日

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Debangkana Dutta,
Moutusi Manna

摘要

Lipid bilayers form topologically distinct phases depending on their composition, which regulate biological functions and define material properties. Cholesterol profoundly influences the fluid-to-gel phase transition in model phospholipid bilayers; however, its impact on the pre-transition ripple phase remains less defined and debated. Here we employed extensive all-atom simulations of pure dipalmitoylphosphatidylcholine (DPPC) and DPPC–cholesterol bilayers (with 15–30 mol% of cholesterol) at 30°C to investigate the rippling characteristics and cholesterol’s effect on their stability and organization in a concentration-dependent manner. Our results delineate the spontaneous formation of an asymmetric ripple pattern in the DPPC bilayer, having a periodic array of gel-like “major” and fluid-like “minor” arms. While the major arm is thick and ordered, and the minor arm is thinner and disordered with significant acyl chain splay and interdigitation, resulting in localized loss of bilayer structure and corrugated surface. Incorporation of cholesterol removes interdigitation and reduces the proportion of highly disordered lipids due to the ordering effect while also impeding acyl chain crystallization. At 15 mol%, cholesterol shows greater tendency to accumulate into relatively disordered domains that coexist with cholesterol-poor ordered domains. Thus, the peristaltic asymmetry of ripple pattern in absence of cholesterol transforms into symmetric ripple keeping the bilayer architecture intact. With increasing cholesterol concentration between 20 and 25 mol%, ripple periodicity causing bilayer undulation decreases gradually and at 30 mol% the bilayer turns into lamellar structure with homogeneous liquid-ordered phase and uniform cholesterol distribution. The present work comprehensively shows the effects of varying cholesterol concentrations on ripple nature and architecture of DPPC bilayer, and provides detailed atomistic insights into how cholesterol modulates the lipid organizations of different domains, acyl chain conformations, and lipid–lipid interactions driving to such transformation, adding to bridge the current gap in understanding cholesterol’s role in ripple phase regulation.

Graphical abstract

We characterized the ripple configuration of DPPC bilayer, which consists of a gel like major domain and also fluid like minor domain with interdigitation between leaflets and highly melted fatty acid chains. With addition of cholesterol, on concentration dependent manner, the ripple pattern of DPPC disrupts and with gradual addition of cholesterol the bilayer transforms into liquid-ordered phase.