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

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

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

Spectrochim Acta A Mol Biomol Spectrosc. 2016 Jun 18;169:175-181

Authors: Chaves OA, Jesus CS, Cruz PF, Sant'Anna CM, Brito RM, Serpa C

Abstract
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~4.34×10(3)M(-1)) and thus can be considered a relatively weak binder. The corresponding thermodynamic parameters: ?G°, ?S° and ?H° showed that the binding process is spontaneous and entropy driven. Results of (1)H 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.


PMID: 27376757 [PubMed - as supplied by publisher]



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