DISULFIDE BRIDGE STRUCTURE OF THE HEAT-STABLE SWEET PROTEIN MABINLIN-II

The heat-stable sweet protein mabinlin was composed of a A-chain of 33 amino-acid residues and a B-chain of 72 amino-acid residues (Liu, X., Maeda, S., Hu, Z., Aiuchi, T., Nakaya, K. and Kurihara, Y. (1993) Eur . J. Biochem. 211, 281-287). A-chain and B-chain contain two and six c ysteine residues, respectively. The formation of two interchain disulf ide bridges at Cys(A5)-Cys(B21) and Cys(A18)-Cys(B10), and two intrach ain disulfide bridges at Cys(B11)-Cys(B59) and Cys(B23)-Cys(B67) were determined by amino-acid sequencing and composition analysis of cystin e-containing peptides isolated by HPLC. Cleavage of the disulfide brid ges with dithiothreitol results in complete loss of the sweet activity of mabinlin II. It was suggested that the structure fixed by four dis ulfide bridges contributes to heat stability of mabinlin II.