Expression, purification and initial characterization of the recombinant storage protein precursor of Theobroma cacao

The gene encoding the 67-kDa cocoa storage protein precursor has been cloned from Theobroma cacao and expressed in Escherichia coli using the pET expression system. The recombinant storage protein has been renatured from inclusion bodies at 30 degrees C using 20 mM glycine-NaOH buffer, pH 10.0, containing 1 mM oxidized glutathione and 0.1% Brij. The renatured protein was purified and demonstrated to adopt a stable native conformation by optical spectroscopy. Secondary structure analysis from circular dichroism indicated the protein to be 23% alpha-helix and 38% beta-sheet, in close agreement with values obtained using a secondary structure prediction program.