Evaluation by fluorescence, STD-NMR, docking and semi-empirical calculations of the o-NBA photo-acid interaction with BSA

• Published in: Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy Molecular and biomolecular spectroscopy, 2016-12, Vol.169, p.175-181
• Main Authors: Chaves, Otávio A., Jesus, Catarina S.H., Cruz, Pedro F., Sant'Anna, Carlos M.R., Brito, Rui M.M., Serpa, Carlos
• Format: Article
• Language: English
• Subjects: Bovine serum albumin; Fluorescence; Molecular docking; o-NBA; pH-jump; STD-NMR
• ISSN: 1386-1425
• DOI: 10.1016/j.saa.2016.06.028

Serum albumins present reversible pH dependent conformational transitions. A sudden laser induced pH-jump is a methodology that can provide new insights on localized protein (un)folding processes that occur within the nanosecond to microsecond time scale. To generate the fast pH jump needed to fast-trigger a protein conformational event, a photo-triggered acid generator as o-nitrobenzaldehyde (o-NBA) can be conveniently used. In order to detect potential specific or nonspecific interactions between o-NBA and BSA, we have performed ligand-binding studies using fluorescence spectroscopy, saturation transfer difference (STD) NMR, molecular docking and semi-empirical calculations. Fluorescence quenching indicates the formation of a non-fluorescent complex in the ground-state between the fluorophore and the quencher, but o-NBA does not bind much effectively to the protein (Ka~4.34×103M−1) and thus can be considered a relatively weak binder. The corresponding thermodynamic parameters: ΔG°, ΔS° and ΔH° showed that the binding process is spontaneous and entropy driven. Results of 1H STD-NMR confirm that the photo-acid and BSA interact, and the relative intensities of the signals in the STD spectra show that all o-NBA protons are equally involved in the binding process, which should correspond to a nonspecific interaction. Molecular docking and semi-empirical calculations suggest that the o-NBA binds preferentially to the Trp-212-containing site of BSA (FA7), interacting via hydrogen bonds with Arg-217 and Tyr-149 residues. [Display omitted] •Binding between BSA and o-NBA was investigated by spectroscopy and theoretical methods.•The binding is relatively weak and entropically driven, possibly related to desolvation effects.•Trp-212-containing site is the main binding site and hydrogen bonding is the main binding force.•Protein-photo-acid interaction indicates that o-NBA can be used in fast induced conformational change studies in BSA.