1H resonance assignments, secondary structure and general topology of single-chain monellin in solution as determined by 1H 2D-NMR.

We determined the resonance assignments, secondary structure and general topology of the 11-kDa sweet protein single-chain monellin (SCM), using two-dimensional proton nuclear magnetic resonance spectroscopy (2D-NMR). SCM is a genetically engineered protein whose design is based on the crystal structure of natural, two-chain monellin (Kim et al., 1989). Analysis of the NMR spectra shows that the secondary structure of SCM consists of a five-strand anti-parallel beta-sheet and a 15-residue alpha-helix. Tertiary NOE constraints place the alpha-helix on the hydrophobic side of the beta-sheet, and indicate that the sheet is partially wrapped around the helix. The general structural features determined for SCM are similar to those of native monellin (Ogata et al., 1987). Some differences between the SCM structure in solution and the crystal structure of monellin are discussed.