SOLID-PHASE SYNTHESIS AND CRYSTALLIZATION OF [ASN22, GLN25, ASN26]-A-CHAIN-[ASN49, GLU50]-B-CHAIN-MONELLIN, AN ANALOG OF THE SWEET PROTEIN MONELLIN

The sweet protein monellin consists of two noncovalently associated polypeptide chains, the A chain of 44 amino acid residues and the B chain of 50 residues. The [Asn22, Gln25, Asn26]-A chain, an analogue of the A chain, was synthesized by the stepwise Fmoc-solid-phase method in an overall yeild of 13.4%. The synthetic A chain analogue was combined with the [Asn49, Glu50]-B chain, which was left over from a previous work, to give [Asn22, Gln25, Asn26]-A-chain-[Asn49, Glu50]-B-chain-monellin in a yeild of 26.2%. This synthetic monellin analogue was approximately 550 times sweeter than sucrose. Changing the carboxyl groups of Asp22, Glu25 and Asp26 of the A chain to amide groups significantly decreased the sweetness potency. Crystallization was performed by a vapor diffusion method.