# Metallo-coiled Coil Stabilization via Chemical Cross-Linking: Implications for Gd(III)-Based MRI Contrast Agents

## TL;DR

Researchers improved the stability of metal-binding protein structures, which could lead to better MRI contrast agents.

## Contribution

A covalent cross-linking strategy is introduced to enhance the stability and performance of metallo-coiled coils for MRI.

## Key findings

- Cross-linking increases metal-binding affinity by 2.5 × 108-fold.
- Cross-linked coiled coils show improved thermal, thermodynamic, and proteolytic stability.
- Optimized cross-linking improves MRI efficacy by ∼30% at clinical field strengths.

## Abstract

Coiled coils are
a versatile class of protein-inspired metal-binding
ligands with well-defined sequence-to-structure relationships and
high synthetic accessibility, making them promising tunable ligands
for applications spanning biomedical imaging, catalysis, and material
science. However, their practical utility is often limited by poor
stability, particularly under physiological conditions. Herein, we
introduce a covalent interhelical isopeptide cross-linking strategy
that significantly enhances the thermal, thermodynamic, kinetic, and
proteolytic stability of lanthanide-bound coiled coils designed for
use as MRI contrast agents. Biophysical analysis, including CD, native
MS, HPLC, and fluorescence assays, reveal that introduction of a single
cross-linking layer promotes structural organization, driving the
peptide from an unfolded to a well-folded state. Cross-linking leads
to a remarkable 2.5 × 108-fold enhancement in metal-binding
affinity, along with greater kinetic stability and resistance to proteolytic
degradation compared to the non-cross-linked analogue. 1H relaxometric studies and molecular dynamics simulations reveal
that this class of potential MRI contrast agents operates via a second-sphere
water coordination mechanism. Optimized cross-linking improves MRI
efficacy by ∼30% at clinically relevant field strengths, highlighting
its potential as a design principle for next-generation MRI contrast
agents. Beyond MRI, these findings underscore the broader potential
of covalent cross-linking strategies for enhancing the stability and
functionality of metallo-coiled coils, expanding their utility across
diverse applications.