β-Sheet Structures Enhance Aggregation-Induced Emission Signals in Peptide-Based Coacervates

Area of Science:

• Biomaterials Science
• Supramolecular Chemistry
• Peptide Self-Assembly

Background:

• Phase-separating peptides (PSPs) form coacervates with potential in bioimaging and drug delivery.
• Understanding the structure-function relationship of PSPs is crucial for optimizing coacervate properties.
• Aggregation-induced emission (AIE) reporters offer a method to probe peptide behavior during coacervation.

Purpose of the Study:

• To investigate the impact of beta-sheet promoting sequences on the coacervation of peptides.
• To characterize the coacervate properties, including size and AIE intensity, influenced by peptide sequence and environmental factors.
• To assess the potential of these coacervates for intracellular labeling.

Main Methods:

• Synthesis of anionic Asp-peptide (D10) and cationic Arg-peptide (R10) conjugated to an AIEgen (PyTPE).
• Incorporation of various beta-sheet promoting peptide spacers (F2G2, W2G2, FFVLK, GFFYK) between the AIEgen and R10.
• Characterization of coacervate formation and properties under varying peptide concentrations, charge ratios, pH, and ionic strength.
• Evaluation of intracellular labeling efficiency and cell viability in MC38 cells.

Main Results:

• Coacervate properties are sensitive to peptide sequence, charge ratio, concentration, pH, and ionic strength.
• Optimal conditions for 100% peptide complexation include 10 mM phosphate buffer, pH 4-12, 0.8 mM total charge equivalent concentration, and a 0.5 charge ratio (R10/D10).
• Peptides with the FFVLK sequence showed the highest AIE (approx. 450-fold) and formed self-coacervates, while W2G2 had minimal effect.
• Coacervates successfully labeled MC38 cells via caveolae-mediated endocytosis with >95% cell viability.

Conclusions:

• Beta-sheet content significantly influences peptide coacervation and AIE properties.
• The FFVLK sequence is a promising motif for developing effective phase-separating peptides for bioimaging applications.
• The developed coacervates demonstrate biocompatibility and efficacy for intracellular labeling.