# Thionin

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{{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](/source/higher_plants). Typically, a thionin consists of 45–48 [amino acid](/source/amino_acid) residues. 6–8 of these are [cysteine](/source/cysteine) forming 3–4 [disulfide bonds](/source/disulfide_bonds). They include [phoratoxin](/source/phoratoxin)s and [viscotoxin](/source/viscotoxin)s.

Alpha- and beta- thionins are related to each other. The [gamma thionin](/source/gamma_thionin)s 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](/source/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](/source/crambin) from the Abyssinian kale (''[Crambe abyssinica](/source/Crambe_abyssinica)'') is also a member of the thionin family.<ref name="PUB00000146" /> Some thionins have [cytotoxic](/source/cytotoxic) activity and they are therefore interesting in the development of new  [drugs](/source/drugs) against [cancer](/source/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 ==
*[Crambin](/source/Crambin)s
*[Gamma thionin](/source/Gamma_thionin)s
*[Antimicrobial peptide](/source/Antimicrobial_peptide)s

== References ==
{{reflist}}

{{Membrane proteins}}

Category:Peripheral membrane proteins
Category:Plant toxins
Category:Antimicrobial peptides

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Adapted from the Wikipedia article [Thionin](https://en.wikipedia.org/wiki/Thionin) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Thionin?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.