# Membrane Pore Formation Unveiled by ∞RETIS Path Sampling: From Thinning to Flip-Flop

## TL;DR

This paper uses a new simulation method to reveal how pores form in cell membranes, showing that thinning and lipid flip-flop are key steps.

## Contribution

The paper introduces ∞RETIS path sampling to study pore formation, revealing new mechanistic insights previously unattainable with conventional methods.

## Key findings

- Pore nucleation is driven by early-stage membrane thinning.
- Lipid flip-flop occurs exclusively via local membrane thinning.
- Pore closure often leads to asymmetric lipid distributions.

## Abstract

Pore formation in lipid bilayers plays a vital role in
membrane
fusion, transport, and signaling. Yet, its detailed mechanism remains
elusive due to the limitations of conventional simulation methods.
To overcome this, we apply a newly developed path sampling technique,
the asynchronous and infinite swap version of Replica Exchange Transition
Interface Sampling (∞RETIS), to study pore formation in a dimyristoylphosphatidylcholine
(DMPC) bilayer modeled with the CHARMM36m force field. Our results
reveal a sequence of tightly coupled events: pore nucleation sites
are determined by early-stage thinning, and the progress into a metastable
pore requires a combination of polar defects and close proximity between
lipids across opposite leaflets. Using Inf-init,
an initiation protocol based on ∞RETIS, rare trajectories can
be generated starting directly from equilibrium simulations. Inf-init and ∞RETIS simulations reveal that lipid
flip-flop occurs exclusively via local membrane thinning, and pore
closure often results in asymmetric lipid distributions.