Thionin

Thionins 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. They include phoratoxins and viscotoxins.

Not to be confused with Thionine or Gamma thionin.
Plant thionin
Wheat beta-purothionin. Alpha helices in red, beta sheets in blue, disulphide bridges in yellow. PDB: 1BHP​
Identifiers
SymbolThionin
PfamPF00321
InterProIPR001010
PROSITEPDOC00244
SCOP21cnb / SCOPe / SUPFAM
TCDB1.C.44
OPM superfamily140
OPM protein2plh
Available protein structures:
Pfam  structures / ECOD  
PDBRCSB PDB; PDBe; PDBj
PDBsumstructure summary
PDB1BHP

Alpha- and beta- thionins are related to each other. The gamma thionins have a superficially similar structure but are an unrelated class of protein, now called plant defensins.

Activity

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.[1] 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.[2] The hydrophobic protein crambin from the Abyssinian kale (Crambe abyssinica) is also a member of the thionin family.[1] Some thionins have cytotoxic activity and they are therefore interesting in the development of new drugs against cancer with novel action mechanisms.[3] No thionin has yet been developed into an anti-cancer drug. Thionin is also a minor protein found in mustard (Brassica napus L.) seeds.[4]

Databases

A database for antimicrobial peptides, including thionins is available: PhytAMP.[5]

See also

References
  1. 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.
  2. 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. S2CID 31727379.
  3. 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. S2CID 5814475.
  4. Bérot S; Compoint JP; Larré C; Malabat C; Guéguen J. (2005). "Large scale purification of rapeseed proteins (Brassica napus L.)". Journal of Chromatography B. 818 (1): 35–42. doi:10.1016/j.jchromb.2004.08.001. PMID 15722042.
  5. "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.
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