Abstract

Calothrixin A ( CLA ), as a carbazole-1,4-quinone alkaloid with unique indolo [3,2- j ] phenanthridine framework, is a natural metabolite from the Calothrix cyanobacteria . Since the interaction to the functional serum albumins may play an important role in estimating its potential physiological or toxicological effects in vivo , we here explored the binding information of CLA with human serum albumin (HSA) by multi-spectroscopic experiments and computational approaches. The molecular docking results showed that there was one binding site of CLA to the site I (subdomain IIA) of HSA, causing the spontaneous formation of the ground state complex of CLA -HSA through the integration of hydrogen bond , hydrophobic interaction, and electrostatic interaction. Moreover, CLA could effectively trigger the change of HSA's secondary structure because of an obvious decrease of α-helical content in HSA. Taking into consideration of the crucial role of HSA to transport extraneous functional small molecules in vivo , this study may provide a worthy theoretical basis to evaluate the in vivo toxicity of CLA , aiming to reduce/avoid the potential toxic side effects of CLA in the next hit-to-lead campaign.