# Dynamics and Structural Responses to Cis–Trans Isomerization in Bacterial Lipid Bilayers

## TL;DR

This paper studies how bacterial membranes adapt to stress by changing fatty acid isomerization, using simulations to explore effects on membrane properties.

## Contribution

The study introduces a molecular dynamics model to quantify the effects of cis–trans isomerization on bacterial membrane structure and dynamics.

## Key findings

- Cis fatty acids have higher probability of unsaturation sites reaching the membrane surface compared to trans fatty acids.
- Cis–trans isomerization affects membrane thickness and lipid diffusion.
- Reduced surface unsaturation in trans fatty acids may impact enzymatic activity and membrane protein function.

## Abstract

Bacterial and eukaryotic cells must respond to a changing
environment
and have multiple adaptive mechanisms to respond to environmental
stresses. Exogenous stresses, such as temperature fluctuations and
osmotic pressure, are known to influence cell membrane fluidity and
gene expression. To maintain membrane homeostasis, Gram-negative bacteria
show a short-term membrane composition response to temperature changes.
Specifically, these bacteria isomerize unsaturated fatty acid tails
in their bilayers, switching unsaturation sites from the more common
cis isomer to the trans isomer. Cis–trans isomerization in
unsaturated fatty acids increases cell membrane rigidity, decreasing
the fluidity of the lipid acyl tails. These changes maintain membrane
homeostasis, but the effect size is difficult to quantify in vivo. In this work, we explore the impact of fatty acid
cis–trans isomerization on the properties and dynamics in a
membrane model based on Pseudomonas putida using molecular dynamics (MD) simulation. In our hypothetical model,
we convert between all-cis and all-trans membranes and report on the
variation in membrane properties under these conditions. In addition
to changes in membrane thickness and lipid diffusion, we find that
the unsaturation site for a cis fatty acid has a higher probability
of coming to the membrane surface than the equivalent trans fatty
acid. The reduced availability of unsaturation sites on the membrane
surface may have downstream implications for their accessibility to
enzymatic attack, potentially influencing the activity of cis–trans
isomerase and other peripheral membrane proteins that act on lipid
unsaturations. Since cis–trans isomerization can occur rapidly
without new lipid biosynthesis, natural selection has adopted cis–trans
isomerization as one of many responses to environmental stress.