Self-coacervation of modular squid beak proteins - a comparative study.

Area of Science:

• Biomaterials Science
• Protein Chemistry
• Materials Engineering

Background:

• The Humboldt squid beak is a natural composite with remarkable stiffness and hardness gradients.
• Its unique properties stem from chitin and protein interactions, particularly protein coacervates.
• Understanding beak proteins is key to mimicking these advanced biomaterials.

Purpose of the Study:

• To investigate the self-coacervation behavior of histidine-rich beak proteins (HBPs) from the Humboldt squid.
• To elucidate the molecular mechanisms governing HBP self-assembly and coacervate formation.
• To explore the potential of HBPs for designing novel biomimetic materials.

Main Methods:

• Studied two histidine-rich beak proteins (HBP-1 and HBP-2) involved in beak bio-fabrication.
• Analyzed protein self-coacervation under varying pH and ionic strength conditions.
• Investigated protein structure, dynamics in solution, and coacervate rheology.

Main Results:

• Both HBPs exhibit intrinsic self-coacervation driven by C-terminal sequence modularity.
• Self-coacervation is modulated by external factors like pH and ionic strength.
• HBPs show dynamic structures in solution, with maximum folding in the coacervate state, driven by hydrophobic interactions.
• Minor variations in HBP repeat sequences significantly alter coacervate rheology.

Conclusions:

• Humboldt squid beak proteins (HBPs) self-assemble into coacervates, contributing to the beak's mechanical properties.
• The self-coacervation mechanism is sensitive to sequence and environmental conditions.
• This research provides insights for designing self-coacervating polypeptides for bio-inspired materials, hydrogels, adhesives, and implants.