# Improving the Activity and Selectivity of a Scorpion-Derived Peptide, A3a, against Acinetobacter baumannii through Rational Design

## TL;DR

Scientists improved a scorpion-derived peptide to better kill antibiotic-resistant bacteria using computer simulations and experiments.

## Contribution

A rational design strategy using MD simulations to enhance AMP activity and selectivity against Acinetobacter baumannii.

## Key findings

- Two novel AMP analogues showed increased potency and selectivity against Acinetobacter baumannii.
- A3a[I14W] demonstrated the highest antibacterial potency and selectivity.
- MD simulations helped explain how structural changes affect peptide function.

## Abstract

The rise in antimicrobial resistance has led to an increased
desire
to understand how antimicrobial peptides (AMPs) can be better engineered
to kill antibiotic-resistant bacteria. Previously, we showed that
C-terminal amidation of a peptide, identified in scorpion Androctonus amoreuxi venom, increased its activity
against both Gram-positive and -negative bacteria. Here, we incorporate
all-atom molecular dynamics (MD) simulations in a rational design
strategy to create analogues of A3a with greater therapeutic potential.
We discover two novel AMPs which achieve greater potency against,
and selectivity toward, Acinetobacter baumannii ATCC 19606 but via two distinct mechanisms and which are effective
in Galleria mellonella models of A. baumannii burn wound infection. While CD spectroscopy
indicates A3a adopts an α-helix conformation in the presence
of models of the Gram-negative bacterial plasma membrane, MD simulations
reveal it adopts a hairpin conformation during initial binding. Three
different strategies, designed to stabilize this hairpin conformation,
produce substantially different outcomes. Deletion of Ile6 and Ile10
restricts conformational flexibility, characteristic of A3a, during
membrane binding, prevents adoption of the α-helix conformation
in the steady state, and abrogates the antibacterial activity. In
contrast, substitution of arginine 7 to lysine (A3a[R7K]) or isoleucine
14 to tryptophan (A3a[I14W]) does not consistently affect peptide
conformations. Both of these new analogues are rapidly bactericidal
toward A. baumannii ATCC 19606 but
A3a[R7K] also causes rapid permeabilization and while the antibacterial
potency and selectivity are increased for both peptides, this is greatest
for A3a[I14W]. Integration of atomistic MD simulations into a multidisciplinary
approach to understanding antimicrobial peptide mechanism of action
is a valuable tool for interpreting the effects of rational design
strategies.