Molecular Mechanisms of the Ultra-Strong Inhibition Effect of Oxidized Carbon Dots on Human Insulin Fibrillation

Area of Science:

• Biochemistry
• Materials Science
• Nanotechnology

Background:

• Protein amyloid fibrillation is linked to various pathological conditions.
• Existing inhibitors often target only early stages of protein aggregation.
• Understanding inhibitor-protein interactions is crucial for therapeutic development.

Purpose of the Study:

• To investigate the relationship between carbon dot (CD) surface properties and their inhibition of human insulin (HI) fibrillation.
• To explore the impact of oxidation on CD functional groups and their inhibitory efficacy.
• To elucidate the binding mechanisms of CDs with HI monomers.

Main Methods:

• Oxidation of carbon dots (CDs) to introduce oxygen-containing functional groups (-OH, -COOH).
• Assessing inhibition of human insulin (HI) fibrillation using fluorescence spectra.
• Isothermal titration calorimetry (ITC) to quantify binding affinities.
• Molecular dynamics (MD) simulations to analyze binding interactions.

Main Results:

• Oxidized CDs, particularly 10-1 CDs (10:1 CD/KMnO4 ratio) with high carboxyl content, demonstrated superior inhibition of HI fibrillation across all stages (nucleation, growth, final).
• Unoxidized CDs showed only weak inhibition at the nucleation stage.
• 10-1 CDs exhibited significantly stronger binding with HI monomers compared to unoxidized CDs.
• MD simulations indicated stronger binding of carboxyl-rich CDs to HI monomers, primarily via electrostatic interactions with histidine residues on the B-chain.

Conclusions:

• Surface carboxyl groups on oxidized CDs are critical for potent inhibition of human insulin fibrillation.
• Oxidized CDs offer a promising strategy for inhibiting protein aggregation by targeting specific protein chains.
• The findings provide insights into designing advanced nanomaterials for therapeutic applications against amyloid diseases.