Molecular mechanism of Ca2 +-catalyzed fusion of phospholipid micelles

Hui Hsu Gavin Tsai, Wei Fu Juang, Che Ming Chang, Tsai Yi Hou, Jian Bin Lee

Research output: Contribution to journalArticlepeer-review

6 Scopus citations

Abstract

Although membrane fusion plays key roles in intracellular trafficking, neurotransmitter release, and viral infection, its underlying molecular mechanism and its energy landscape are not well understood. In this study, we employed all-atom molecular dynamics simulations to investigate the fusion mechanism, catalyzed by Ca2 + ions, of two highly hydrated 1-palmitoyl-2-oleoyl-sn-3-phosphoethanolamine (POPE) micelles. This simulation system mimics the small contact zone between two large vesicles at which the fusion is initiated. Our simulations revealed that Ca2 + ions are capable of catalyzing the fusion of POPE micelles; in contrast, we did not observe close contact of the two micelles in the presence of only Na+ or Mg2 + ions. Determining the free energy landscape of fusion allowed us to characterize the underlying molecular mechanism. The Ca 2 + ions play a key role in catalyzing the micelle fusion in three aspects: creating a more-hydrophobic surface on the micelles, binding two micelles together, and enhancing the formation of the pre-stalk state. In contrast, Na+ or Mg2 + ions have relatively limited effects. Effective fusion proceeds through sequential formation of pre-stalk, stalk, hemifused-like, and fused states. The pre-stalk state is the state featuring lipid tails exposed to the inter-micellar space; its formation is the rate-limiting step. The stalk state is the state where a localized hydrophobic core is formed connecting two micelles; its formation occurs in conjunction with water expulsion from the inter-micellar space. This study provides insight into the molecular mechanism of fusion from the points of view of energetics, structure, and dynamics.

Original languageEnglish
Pages (from-to)2729-2738
Number of pages10
JournalBiochimica et Biophysica Acta - Biomembranes
Volume1828
Issue number11
DOIs
StatePublished - 2013

Keywords

  • Ca2 + -lipid cluster
  • Free energy landscape
  • Fusion mechanism
  • Membrane fusion
  • Pre-stalk state
  • Stalk state

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