Glycation reduces the binding dynamics of aflatoxin B₁ to human serum albumin: a comprehensive spectroscopic and computational investigation

Abstract

Aflatoxin B₁ (AFB₁), a potent mutagen, is synthesized by Aspergillus parasiticus and Aspergillus flavus. Human serum albumin (HSA) is a globular protein with diverse roles. As AFB₁ is ingested with food and is transported in the body via blood, it becomes pertinent to comprehend the effect of the binding of this toxin on the structure and conformation of HSA, which may help to get insight into the toxic effect of the exposure of the mycotoxin. In this study, multi-spectroscopic approaches have been used to evaluate the binding efficiency of AFB₁ with both the native HSA (nHSA) and the glycated HSA (gHSA). Steady-state fluorescence spectroscopy reveals the static type of fluorescence quenching in the fluorescence emission spectra of nHSA and gHSA in the presence of AFB₁. The binding constant (K_b) is calculated to be 6.88 × 10⁴ M⁻¹ for nHSA, while a reduced K_b value of 2.95 × 10⁴ M⁻¹ has been obtained for gHSA. The circular dichroism study confirms the change in the secondary structure of nHSA and gHSA in the presence of AFB₁, followed by alterations in the melting temperature (T_m) of nHSA and gHSA. In silico computational findings envisaged the amino acid residues and bonds involved in the binding of nHSA and gHSA with AFB₁. The comprehensive study analyzes the binding effectiveness of AFB₁ with nHSA and gHSA and shows reduced binding of AFB₁ to gHSA.

Communicated by Ramaswamy H. Sarma

HIGHLIGHTS

• As revealed by UV-absorption spectroscopy, the hyperchromic effect was more prominent in nHSA than gHSA in the presence of AFB₁.

• The binding constant (K_b) obtained for the nHSA-AFB₁ complex was 6.88 × 10⁴ M^−1, and the gHSA-AFB₁ complex yielded K_b value of 2.95 × 10⁴ M⁻¹.

• Negative enthalpy change (ΔH) and entropy change (ΔS) suggested hydrogen bonding and van der Waals interaction as stabilizing forces of nHSA-AFB₁ and gHSA-AFB₁ complex.

• Site markers displacement assay suggested Sudlow’s site I as the binding site for AFB₁ in nHSA and gHSA.

• Circular dichroism study showed that AFB₁ induced secondary structural changes in nHSA and gHSA.

• Melting temperature (T_m) increased in nHSA and decreased in gHSA in the presence of AFB₁.

• Molecular docking results confirmed Lys-195, Arg-222 and Arg-257 as hydrogen bonding residues in the nHSA-AFB₁ complex and Arg-222 and Lys-199 residues were involved in hydrogen bonding in the gHSA-AFB₁ complex.

Keywords:

• Aflatoxin B₁
• human serum albumin
• glycation
• spectroscopy
• fluorescence

Acknowledgements

The authors are thankful to DST, UGC, and Aligarh Muslim University for providing necessary support. MAQ is grateful to the ICMR, New Delhi, India, for providing a Senior Research Fellowship (ID: 2019-6985)

Disclosure statement

The authors declare that there is no conflict of interest.

Additional information

Funding

Mohd Aamir Qureshi received Senior Research Fellowship from the Indian Council of Medical Research (ID: 2019-6985). Apart from this present research did not receive any specific grant from any funding agencies in the public, commercial, or not-for-profit sectors.