Fabrication of stable spherical soybean lipophilic protein nanogel for curcumin delivery: Carbony oxygen and aromatic ring flexibility binding to the beta−barrel

Abstract

Soybean lipophilic protein (SLP), which comprises approximately 10 % polar lipids (especially phosphatidylcholine (PC)) in glycinin (11S) and β-conglycinin (7S), is a potentially effective delivery for nutraceuticals. Herein, we successfully engineered a stable spherical soybean lipophilic protein nanogel through a pH−shift treatment at its isoelectric point, designed for the efficient delivery of curcumin (Cur) to enhance its bioavailability. The analysis of the physicochemical and structural properties of the SLP−nanogel revealed its exceptional encapsulation efficiency, achieving 93.52 %, surpassing that of soybean isolated protein at 83.67 %. Moreover, the loading ability experienced a remarkable 8.7−fold increase, reaching 13.02 μg/mg. Fluorescence kinetics analysis reveals that Cur selectively binds to a single site on 7SPC/11SPC, predominantly through van der Waals forces and hydrogen bonds. Molecular dynamics results revealed that the pH−shifted treatment expanded the beta−barrel volume of 7SPC/11SPC, enhancing the binding affinity between 7SPC/11SPC and Cur by forming H−bonds and pi−H interaction in the beta−barrel regions of K232−Y388 (7SPC) and D300−I410 (11SPC). Our findings provided a novel and effective way to prepare stable spherical nanogels for delivering Cur and a novel insight into the binding mechanism between Cur and 11SPC/7SPC.