Interaction of rS1-Casein with Curcumin and Its Biological Implications

RS1-Casein is one of the major protein components of the casein fraction of milk. Curcumin
(diferuloyl methane), the major curcuminoid, constituting about 2-5% of turmeric (Curcuma longa)
is the active ingredient with many physiological, biochemical, and pharmacological properties. On
the basis of spectroscopic measurements, it is inferred that curcumin binds to RS1-casein at pH 7.4
and 27 �C with two binding sites, one with high affinity [(2.01 ( 0.6) � 106 M-1] and the other with
low affinity [(6.3 ( 0.4) � 104 M-1]. Binding of curcumin to RS1-casein is predominantly hydrophobic
in nature. The anisotropy of curcumin or conformation of RS1-casein did not change on interaction.
The stability of curcumin in solution at pH 7.2 was enhanced on binding with RS1-casein. The
chaperone-like activity of RS1-casein gets slightly enhanced on its binding to curcumin. The ability of
curcumin to protect erythrocytes against hemolysis was not affected due to curcumin- RS1-casein
interaction. The two binding sites of RS1-casein for curcumin, along with enhanced solution stability
on interaction, may offer an alternative approach in physiological and nutritional applications.