{{Distinguish|Thionine|Gamma thionin}} {{Infobox protein family | Symbol = Thionin | Name = Plant thionin | image =Beta thionin.png | width = | caption = Wheat beta-purothionin. Alpha helices in red, beta sheets in blue, disulphide bridges in yellow. {{PDB|1BHP}} | Pfam= PF00321 | InterPro= IPR001010 | SMART= | PROSITE = PDOC00244 | SCOP = 1cnb | TCDB = 1.C.44 | OPM family= 140 | OPM protein= 2plh | PDB=1BHP }}
'''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.
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.<ref name="PUB00000146">{{cite journal |vauthors=Vernon LP, Evett GE, Zeikus RD, Gray WR |title=A toxic thionin from Pyrularia pubera: purification, properties, and amino acid sequence |journal=Arch. Biochem. Biophys. |volume=238 |issue=1 |pages=18–29 |year=1985 |pmid=3985614 |doi=10.1016/0003-9861(85)90136-5}}</ref> 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.<ref name="PUB00004552">{{cite journal |vauthors=Apel K, Andresen I, Becker W, Schluter K, Burges J, Parthier B |title=The identification of leaf thionin as one of the main jasmonate-induced proteins of barley (Hordeum vulgare) |journal=Plant Mol. Biol. |volume=19 |issue=2 |pages=193–204 |year=1992 |pmid=1377959 |doi=10.1007/BF00027341|bibcode=1992PMolB..19..193A |s2cid=31727379 }}</ref> The hydrophobic protein crambin from the Abyssinian kale (''Crambe abyssinica'') is also a member of the thionin family.<ref name="PUB00000146" /> Some thionins have cytotoxic activity and they are therefore interesting in the development of new drugs against cancer with novel action mechanisms.<ref>{{cite journal |doi=10.1007/BF00039517 |vauthors=Florack DE, Stiekema WJ |title=Thionins: properties, possible biological roles and mechanisms of action |journal=Plant Mol. Biol. |volume=26 |issue=1 |pages=25–37 |date=October 1994 |pmid=7948874 |bibcode=1994PMolB..26...25F |s2cid=5814475 }}</ref> No thionin has yet been developed into an anti-cancer drug. Thionin is also a minor protein found in mustard (Brassica napus L.) seeds.<ref>{{cite journal |author1=Bérot S |author2=Compoint JP |author3=Larré C |author4=Malabat C |author5=Guéguen J.|title=Large scale purification of rapeseed proteins (Brassica napus L.)|doi=10.1016/j.jchromb.2004.08.001 |volume=818 |year=2005 |journal=Journal of Chromatography B |issue=1 |pages=35–42|pmid=15722042 }}</ref>
==Databases== A database for antimicrobial peptides, including thionins is available: PhytAMP.<ref name="pmid18836196">{{cite web | url = http://phytamp.hammamilab.org/ | title = PhytAMP Database | access-date = 2017-06-10 | archive-date = 2022-06-17 | archive-url = https://web.archive.org/web/20220617133608/http://phytamp.hammamilab.org/ | url-status = dead }}; {{cite journal | vauthors = Hammami R, Ben Hamida J, Vergoten G, Fliss I | title = PhytAMP: a database dedicated to antimicrobial plant peptides | journal = Nucleic Acids Res. | volume = 37 | issue = Database issue | pages = D963–8 |date=January 2009 | pmid = 18836196 | pmc = 2686510 | doi = 10.1093/nar/gkn655 }}</ref>
== See also == *Crambins *Gamma thionins *Antimicrobial peptides
== References == {{reflist}}
{{Membrane proteins}}
Category:Peripheral membrane proteins Category:Plant toxins Category:Antimicrobial peptides