# Glycine Composition and Ion Valency Tune Phase Behavior and Drug Encapsulation in Designer Peptide Condensates

## TL;DR

Researchers designed peptide condensates that can encapsulate drugs and release them in response to specific triggers, by tuning factors like glycine content and ion valency.

## Contribution

The study establishes design rules for tuning peptide condensates by linking glycine composition and ion valency to phase behavior and drug encapsulation.

## Key findings

- Glycine-poor peptides form densely packed condensates with larger droplet sizes when exposed to sulfate ions.
- Glycine content influences condensate dynamics, with higher glycine leading to faster diffusion.
- Compound-specific and salt-mediated recruitment of FDA-approved drugs into condensates is influenced by hydrophobicity, polarity, and charge state.

## Abstract

Nano- and microencapsulation that combines high loading
capacity
with stimulus-responsive release remains a challenge for therapeutic
delivery. Designed peptide condensates formed by liquid–liquid
phase separation offer a versatile and biocompatible platform to address
this need. Here, we systematically link backbone flexibility and ion
identity to phase behavior, material properties, payload encapsulation,
and protease-triggered condensate disassembly using minimalistic cationic–aromatic
peptides that differ in their glycine content. Moreover, we systematically
studied how monovalent vs divalent anions affect phase behavior and
payload encapsulation. Our results show that glycine-poor sequence
forms the most highly packed condensates and that the kosmotrope divalent
sulfate ions markedly increase dense-phase peptide concentration and
droplet size. Glycine content, which regulates charge density and
backbone flexibility, directly affects condensate dynamics, showing
faster diffusion with an increasing number of glycine residues. High-performance
liquid chromatography partitioning analysis of five FDA-approved small
molecules demonstrates compound-specific and salt-mediated recruitment,
where both the hydrophobicity/polarity and the charge state of the
compounds affect their encapsulation in the dense phase. Moreover,
using trypsin as a proteolytic trigger, we show how the glycine content
affects condensate disassembly. Overall, these results facilitate
practical design rules that show how to tune charge and aromatic density,
backbone flexibility, and ion valency to regulate dense-phase packing,
payload encapsulation, and release. These insights advance the rational
engineering of peptide condensates for targeted sequestration and
controlled therapeutic release.