Caffeine and sulfadiazine interact differently with human serum albumin: A combined fluorescence and molecular docking study

• Interaction of caffeine and sulfadiazine with HSA was studied.
• Intrinsic Trp fluorescence of HSA is quenched by both the drugs.
• Both CAF and SDZ bind to similar site in HSA.
• Thermodynamics and mode of interaction for the drugs with HSA is different.
• Docking calculation supports the fluorescence spectroscopic results.

The interaction and binding behavior of the well-known drug sulfadiazine (SDZ) and psychoactive stimulant caffeine (CAF) with human serum albumin (HSA) was monitored by in vitro fluorescence titration and molecular docking calculations under physiological condition. The quenching of protein fluorescence on addition of CAF is due to the formation of protein–drug complex in the ground state; whereas in case of SDZ, the experimental results were explained on the basis of sphere of action model. Although both these compounds bind preferentially in Sudlow’s site 1 of the protein, the association constant is approximately two fold higher in case of SDZ (∼4.0 × 104 M−1) in comparison with CAF (∼9.3 × 102 M−1) and correlates well with physico-chemical properties like pKa and lipophilicity of the drugs. Temperature dependent fluorescence study reveals that both SDZ and CAF bind spontaneously with HSA. However, the binding of SDZ with the protein is mainly governed by the hydrophobic forces in contrast with that of CAF; where, the interaction is best explained in terms of electrostatic mechanism. Molecular docking calculation predicts the binding of these drugs in different location of sub-domain IIA in the protein structure.

The intrinsic tryptophan fluorescence quenching of HSA in presence of sulfadiazine (SDZ) and caffeine (CAF) reveals the difference in binding of these two drugs in Sudlow’s 1 site.Figure optionsDownload as PowerPoint slide