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 (Kb) is calculated to be 6.88 × 104 M-1 for nHSA, while a reduced Kb 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 (Tm) 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.
Keywords: Aflatoxin B1; fluorescence; glycation; human serum albumin; spectroscopy.
As revealed by UV-absorption spectroscopy, the hyperchromic effect was more prominent in nHSA than gHSA in the presence of AFB1.The binding constant (Kb) obtained for the nHSA-AFB1 complex was 6.88 × 104 M−1, and the gHSA-AFB1 complex yielded Kb 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 (Tm) 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.