Solution structure of gamma 1-H thionin from barley endosperm.
Thionins (without an e) are a family of small proteins found solely in higher plants. Typically, a thionin consists of 45–48 amino acid residues. 6–8 of these are cysteine forming 3–4 disulfide bonds. Some thionins have cytotoxic activity and they are therefore interesting in the development of new drugs against cancer with novel action mechanisms. No thionin has yet been developed into an anti-cancer drug.
The proteins are toxic to animal cells, presumably attacking the cell membrane and rendering it permeable: this results in the inhibition of sugar uptake and allows potassium and phosphate ions, proteins, and nucleotides to leak from cells. Thionins are mainly found in seeds where they may act as a defence against consumption by animals. A barley (Hordeum vulgare) leaf thionin that is highly toxic to plant pathogens and is involved in the mechanism of plant defence against microbial infections has also been identified. The hydrophobic protein crambin from the Abyssinian kale (Crambe abyssinica) is also a member of the thionin family.
Structures of gamma 1-horodthionin and gamma 1-purothionin were determined. The protein consists of an amino acid chain of 47 residues, with the tertiary structure revealing a three stranded, anti-parallel beta sheet, one alpha helix, and the connecting loops. The three strands of the beta sheet are residues 1-6, 31-34, and 39-47, while the alpha helix is residues 16-28. Thionin has a hydrophobic protein core that holds the beta sheet and alpha helix in its three-dimensional structure. Additionally, the protein structure is stabilized by three disulfide bonds, forming a “cysteine-stabilized alpha-helical motif.” The structure of gamma-thionins differs significantly from the plant alpha- or beta-thionins, resembling scorpion toxins or insect defensins.
A database for antimicrobial peptides, including thionins is available: PhytAMP.
- PDB 1GPT; Bruix M, Jiménez MA, Santoro J, González C, Colilla FJ, Méndez E, Rico M (January 1993). "Solution structure of gamma 1-H and gamma 1-P thionins from barley and wheat endosperm determined by 1H-NMR: a structural motif common to toxic arthropod proteins". Biochemistry 32 (2): 715–24. doi:10.1021/bi00053a041. PMID 8380707.
- Florack DE, Stiekema WJ (October 1994). "Thionins: properties, possible biological roles and mechanisms of action". Plant Mol. Biol. 26 (1): 25–37. doi:10.1007/BF00039517. PMID 7948874.
- Vernon LP, Evett GE, Zeikus RD, Gray WR (1985). "A toxic thionin from Pyrularia pubera: purification, properties, and amino acid sequence". Arch. Biochem. Biophys. 238 (1): 18–29. doi:10.1016/0003-9861(85)90136-5. PMID 3985614.
- Apel K, Andresen I, Becker W, Schluter K, Burges J, Parthier B (1992). "The identification of leaf thionin as one of the main jasmonate-induced proteins of barley (Hordeum vulgare)". Plant Mol. Biol. 19 (2): 193–204. doi:10.1007/BF00027341. PMID 1377959.
- "PhytAMP Database".; Hammami R, Ben Hamida J, Vergoten G, Fliss I (January 2009). "PhytAMP: a database dedicated to antimicrobial plant peptides". Nucleic Acids Res. 37 (Database issue): D963–8. doi:10.1093/nar/gkn655. PMC 2686510. PMID 18836196.
|This biochemistry article is a stub. You can help Wikipedia by expanding it.|