| Plant thionin | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| Solution structure of gamma 1-H thionin from barley endosperm.[1] | |||||||||
| Identifiers | |||||||||
| Symbol | Thionin | ||||||||
| Pfam | PF00321 | ||||||||
| InterPro | IPR001010 | ||||||||
| PROSITE | PDOC00244 | ||||||||
| SCOP | 1cnb | ||||||||
| TCDB | 1.C.44 | ||||||||
| OPM protein | 2plh | ||||||||
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Thionins (without an e) can also refer to a family of peptides 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.[2] As of yet, no thionin has ever 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.[3] 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.[4] The hydrophobic protein crambin from the Abyssinian kale (Crambe abyssinica) is also a member of the thionin family.[3]
Based on proton distance NMR, the 3D structure of plant thionin from barley and wheat endosperm have been be derived. Gamma 1-horodthionin and gamma 1-purothionin were analyzed. 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-stablized alpha-helical motif.” The structure of gamma-thionins differs significantly from the plant alpha- or beta-thionins, resembling scorpion toxins or insect defensins.[1]
A database for antimicrobial peptides, including thionins is available: PhytAMP.[5]
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