Protopine and Allocryptopine Interactions with Plasma Proteins.

Area of Science:

• Biochemistry
• Pharmacology
• Natural Products Chemistry

Background:

• Human serum albumin (HSA) and α-1-acid glycoprotein (AAG) are key plasma proteins involved in drug transport.
• Isoquinoline alkaloids, such as allocryptopine (ACP) and protopine (PP), are natural compounds with potential therapeutic applications.

Purpose of the Study:

• To investigate the binding interactions between ACP, PP, and the plasma proteins HSA and AAG.
• To elucidate the binding sites and affinity of these alkaloids to HSA and AAG.
• To assess the impact of alkaloid binding on protein structure.

Main Methods:

• UV-Vis spectroscopy to monitor complex formation.
• Molecular docking to predict binding sites and interactions.
• Competitive binding assays using specific markers.
• Circular dichroism (CD) spectroscopy to evaluate protein structural changes.

Main Results:

• ACP and PP form spontaneous and stable complexes with both HSA and AAG.
• ACP exhibits a higher binding affinity for both proteins compared to PP.
• Molecular docking identified preferential binding sites on HSA (site 2/IIIA) for both alkaloids.
• Competitive assays and fluorescence quenching confirmed alkaloid displacement of markers on HSA and AAG.
• CD spectroscopy indicated that protein structures remain largely unaltered upon complex formation.

Conclusions:

• ACP and PP interact effectively with HSA and AAG, forming stable complexes.
• The binding affinity is higher for ACP, suggesting potential for targeted delivery or therapeutic modulation.
• The lack of significant structural perturbation implies that these interactions may not lead to protein denaturation.
• Findings contribute to understanding natural product-protein interactions and inform future drug design using isoquinoline alkaloids.