The consequences of adopting therapeutic luminophore azapodophyllotoxin into BSA: a molecular regulator to control emissive population of two tryptophan residues in carrier protein

Abstract

Bovine serum albumin (BSA) is a widely recognized plasma protein for its ubiquitous function as one of the paramount transporter of different drugs and enzymes inside biological systems. HPFQ, a member of azapodophyllotoxin family, has been observed to be highly bioactive against a majority of cancer cell lines; while subsequently showing impressive fluorescent properties throughout the polarity scale. However, further pursuit into compliance of this bioactive fluorophore with carrier protein remains imperative for excavating its suitable transporter inside human body. The present biophysical spectroscopic study attempts to exhibit the adaptability of BSA towards a potential therapeutic fluorophore (HPFQ) by combining in vitro optical spectroscopy and in silico molecular docking. The competitive site-binding studies demonstrated that BSA nurtures neutral anti-cancer fluorophore HPFQ into Sudlow site I, where it experiences varying interactions with surrounding hydrophobic amino acid residues viz. Phe 205, Trp 213, Ala 209, Leu 330, Ala 349, Leu 480 etc. HPFQ gets accommodated at the vicinity of Trp-213 in BSA and initiates operation of FRET between them. Adaptation of HPFQ encourages an allosteric modulation, leading to a minor deformation in secondary protein structure, which probably allows the invading water molecules to increase the micropolarity of the adjacent environment around Trp-213. HPFQ assumes to administer conformational alteration in BSA and regulate emissive population of two tryptophan residues Trp-134 and Trp-213. The amalgamated spectroscopic investigation described herein may encourage design of azapodophyllotoxin based potential therapeutic agents for effective in vivo bio-circulation using BSA-based drug distribution systems.

Communicated by Ramaswamy H. Sarma

Keywords:

• Bovine serum albumin
• carrier protein
• azapodophyllotoxin
• fluorescence quenching
• FRET
• time-resolved fluorescence
• molecular docking

Acknowledgement

The authors express their gratitude towards the Department of Chemistry, VNIT, Nagpur for providing the necessary facilities. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.

Author contributions

SM, KG and AS conducted the majority of the experiments and performed data analyses. SM and SG performed molecular docking studies. AK and SKG designed study, and supervised the project; SM wrote the manuscript, while SKG reviewed the manuscript. SKG is the guarantor of this work and, as such, had full access to all the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.

Disclosure Statement

The authors declare that there are no conflicts of interest.

Additional information

Funding

AK acknowledges National Institutes of Health, as the research reported in this publication was partly supported by an Institutional Development Award (IDeA) from the National Institute of General Medical Sciences of the National Institutes of Health under grant number P20 GM103475-14.