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Ligand binding induces a sharp decrease in hydrophobicity of folate binding protein assessed by 1-anilinonaphthalene-8-sulphonate which suppresses self-association of the hydrophobic apo-protein

Department of Clinical Biochemistry, Hillerød Hospital, Dyrehavevej 29, DK-3400 Hillerød, Denmark.
Biochemical and Biophysical Research Communications (Impact Factor: 2.28). 07/2012; 425(1):19-24. DOI: 10.1016/j.bbrc.2012.07.036
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ABSTRACT High affinity folate binding protein (FBP) regulates as a soluble protein and as a cellular receptor intracellular trafficking of folic acid, a vitamin of great importance to cell growth and division. We addressed two issues of potential importance to the biological function of FBP, a possible decrease of the surface hydrophobicity associated with the ligand-induced conformation change of FBP, and protein-inter-protein interactions involved in self-association of hydrophobic apo-FBP. The extrinsic fluorescent apolar dye 1-anilinonaphthalene-8-sulphonate (ANS) exhibited enhanced fluorescence intensity and a blueshift of emission maximum from 510-520 nm to 460-470 nm upon addition of apo-FBP indicating binding to a strongly hydrophobic environment. Neither enhancement of fluorescence nor blueshift of ANS emission maximum occurred when folate-ligated holo-FBP replaced apo-FBP. The drastic decrease in surface hydrophobicity of holo-FBP could have bearings on the biological function of FBP since changes in surface hydrophobicity have critical effects on the biological function of receptors and transport proteins. ANS interacts with exposed hydrophobic surfaces on proteins and may thereby block and prevent aggregation of proteins (chaperone-like effect). Hence, hydrophobic interactions seemed to participate in the concentration-dependent self-association of apo-FBP which was suppressed by high ANS concentrations in light scatter measurements.

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    • "ANS is an extrinsic fluorescent probe that emits large fluorescence energy at 470 nm when anilinonaphthalene group binds to hydrophobic areas of proteins. ANS has been widely used in numerous investigations to study hydrophobic interactions of proteins (Holm et al., 2012), refolding of proteins (Gautam et al., 2012), protein–ligand interactions (Ding et al., 2010; Tutar et al., 2010), protein aggregation (Bolognesi et al., 2010), protein denaturation (Yadav and Prakash, 2009), protein surface hydrophobicity (Alizadeh-Pasdar and Li-Chan, 2000), and others. Hence, ANS method can be used to quantify superficial hydrophobicity of proteins, previously separated in HIC, in order to analyze its chromatographic behavior when the effect of different parameters in HIC are being studied. "
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