Crystal Structures of the Sweet Protein MNEI: Insights into Sweet Protein-Receptor Interactions

Monellin is one of a small number of highly potent, sweet-tasting proteins. X-ray crystal structures of a wild-type single chain monellin (MNEI) and a 10-fold less sweet mutant (G16A) were determined in order to understand the cause of this reduction in sweetness and gain insight into sweet protein-receptor interactions. Comparison of the two structures reveals little change to the global protein fold. However, alterations of amino acid side chain position and exposure adjacent to the site of mutation result in a reorganization of key functional groups on the surface of MNEI. This finding supports the idea that an extensive surface of monellin is involved in binding the T1R2:T1R3 receptor. (C) 2008 American Chemical Society