Molecule of the Month: Monellin
Monellin and other supersweet proteins trick our taste receptors.
Exploring the Structure
Since it’s so sweet, monellin would be great for creating diet foods, since only a little is needed. However, it rapidly loses its sweetness when heated, so it’s not much good for baking. To solve this problem, researchers have engineered new heat-stable forms of monellin by connecting its two chains. To explore natural monellin (PDB entry 3mon) and two engineered single-chain forms (PDB entries 1mol and 1fa3), click on the image for an interactive JSmol.
Topics for Further Discussion
- Thaumatin is often used as a test system when researchers are developing new methods for protein crystallography, since it is readily available and easily forms crystals. Try searching for “thaumatin” to see some of the ways it has been used.
- The proteins lysozyme and mabinlin also taste sweet, although not as sweet as the proteins shown here—try searching for them to explore their structures.
Related PDB-101 Resources
- Browse Biotechnology
- Browse Biology of Plants
- 4or2: H. Wu, C. Wang, K. J. Gregory, G. W. Han, H. P. Cho, Y. Xia, C. M. Niswender, V. Katritch, J. Meiler, V. Cherezov, P. J. Conn & R. C. Stevens (2014) Structure of a class C GPCR metabotropic glutamate receptor 1 bound to an allosteric modulator. Science 344, 58-64.
- D. Picone & P. A. Temussi (2012) Dissimilar sweet proteins from plants: oddities or normal components? Plant Science 195, 135-142.
- 2e4z: T. Muto, D. Tsuchiya, K. Morikawa & H. Jingami (2007) Structures of the extracellular regions of the group II/III metabotropic glutamate receptors. Proceedings of the National Academy of Science USA 104, 3759-3764.
- P. A. Temussi (2006) Natural sweet macromolecules: how sweet proteins work. Cellular and Molecular Life Sciences 63, 1876-1888.
- 2d04: A. Shimizu-Ibuka, Y. Morita, T. Terada, T. Asakura, K. Nakajima, S. Iwata, T. Misaka, H. Sorimachi, S. Arai & K. Abe (2006) Crystal structure of neoculin: insights into its sweetness and taste-modifying activity. Journal of Molecular Biology 359, 148-158.
- 1fa3: R. Spadaccini, O. Crescenzi, T. Tancredi, N. De Casamassimi, G. Saviano, R. Scognamiglio, A. Di Donato & P. A. Temussi (2001) Solution structure of a sweet protein: NMR study of MNEI, a single chain monellin. Journal of Molecular Biology 305, 505-514.
- 1c4e: J. I. Fletcher, A. J. Dingley, R. Smith, M. Connor, M. J. Christie & G. F. King (1999) High-resolution solution structure of gurmarin, a sweet-taste-suppressing plant polypeptide. European Journal of Biochemistry 264, 525-533.
- 2brz: J. E. Caldwell, F. Abildgaard, Z. Dzakula, D. Ming, G. Hellekant & J. L. Markley (1998) Solution structure of the thermostable sweet-tasting protein brazzein. Nature Structural Biology 5, 427-431.
- 1thv: T. P. Ko, J. Day, A. Greenwood & A. McPherson (1994) Structures of three crystal forms of the sweet protein thaumatin. Acta Crystallographica D50, 813-825.
- 1mol: J. R. Somoza, F. Jiang, L. Tong, C. H. Kang, J. M. Cho & S. H. Kim (1993) Two crystal structures of a potently sweet protein. Natural monellin at 2.75 A resolution and single-chain monellin at 1.7 A resolution. Journal of Molecular Biology 234, 390-404.
- 3mon: Kim S. H., de Vos, A. & Ogata, C. (1988) Crystal structures of two intensely sweet proteins. Trends in Biochemical Sciences 13, 13-15.
July 2016, David Goodselldoi:10.2210/rcsb_pdb/mom_2016_7