Assignment of the disulfide bonds in the sweet protein brazzein

The thermostable sweet protein brazzein consists of 54 amino acid residues and has four intramolecular disulfide bonds, the location of which is unknown. We found that brazzein resists enzymatic hydrolysis at enzyme/substrate ratios (w/w) of 1:100-1:10 at 35-40°Cfor 24-48 h. Brazzein was hydrolyzed using thermolysin at an enzyme/substrate ratio of 1:1 (w/w) in water, pH 5.5, for 6 h and at 50°C. The disulfide bonds were determined, by a combination of mass spectrometric analysis and amino acid sequencing of cystine-containingpeptides, to be between Cys4-Cys52, Cysl6-Cys37, Cys22-Cys47, andCys26-Cys49. These disulfide bonds contribute to its thermostability.