Molecular View of Hexagonal Phase Formation in Phospholipid Membranes

¹ University of Groningen

^* To whom correspondence should be addressed. E-mail: marrink{at}chem.rug.nl.

Submitted on June 30, 2004
Revised on July 19, 2004
Accepted on 2 September 2004

	Abstract

Important biological processes such as vesicle fusion or budding require the cell matrix to undergo a transition from a lamellar to a non-lamellar state. Although equilibrium properties of membranes are amenable to detailed theoretical studies, collective rearrangements involved in phase transitions have thusfar only been modeled on a qualitative level. Here, for the first time, the complete transition pathway from a multilamellar to an inverted hexagonal phase is elucidated at near-atomic detail using a recently developed coarse grained molecular dyanmics simulation model. Insight is provided into experimentally inaccessible data such as the molecular structure of the intermediates and the kinetics involved. Starting from multi-lamellar configurations, the spontaneous formation of stalks between the bilayers is observed on a nanosecond timescale at elevated temperatures or reduced hydration levels. The stalks subsequently elongate in a cooperative manner leading to the formation of an inverted hexagonal phase. The rate of stalk elongation depends on the state conditions, ranging from 1 nm/micros to 1 nm/ns Within a narrow hydration/temprature/composition range the stalks appear stable and rearrange into the rhombohedral phase.

Key Words: coarse grained model, fusion, molecular dynamics, phase transition, simulation, stalk

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