Gamma-thionins are small evolutionarily related proteins

Protein family

A protein family is a group of evolutionarily-related proteins, and is often nearly synonymous with gene family. The term protein family should not be confused with family as it is used in taxonomy....

 of plants that serve to defend them against parasites.

The following plant proteins belong to this family:

• Gamma-thionins from Triticum aestivum (Wheat) endosperm (gamma-purothionins) and gamma-hordothionins from Hordeum vulgare(Barley) are toxic to animal cells and inhibit protein synthesis in cell free systems.
• A flower-specific thionin (FST) from Nicotiana tabacum
  Nicotiana tabacum
  Nicotiana tabacum, or cultivated tobacco, is a perennial herbaceous plant. It is found only in cultivation, where it is the most commonly grown of all plants in the Nicotiana genus, and its leaves are commercially grown in many countries to be processed into tobacco. It grows to heights between 1...
  
  (Common Tobacco).
• Antifungal proteins (AFP) from the seeds of Brassicaceae species such as radish, mustard, turnip and Arabidopsis thaliana
  Arabidopsis thaliana
  Arabidopsis thaliana is a small flowering plant native to Europe, Asia, and northwestern Africa. A spring annual with a relatively short life cycle, arabidopsis is popular as a model organism in plant biology and genetics...
  
  (Thale Cress).
• Inhibitors of insect alpha-amylases from sorghum.
• Probable protease inhibitor P322 from Solanum tuberosum (Potato).
• A germination-related protein from Vigna unguiculata (Cowpea).
• Anther-specific protein SF18 from sunflower. SF18 is a protein that contains a gamma-thionin domain at its N-terminus and a proline-rich C-terminal domain.
• Glycine max (Soybean) sulfur-rich protein SE60.
• Vicia faba
  Vicia faba
  This article refers to the Broad Bean plant. For Broadbean the company, see Broadbean, Inc.Vicia faba, the Broad Bean, Fava Bean, Field Bean, Bell Bean or Tic Bean, is a species of bean native to north Africa and southwest Asia, and extensively cultivated elsewhere. A variety is provisionally...
  
  (Broad bean) antibacterial peptides fabatin-1 and -2.

In their mature form, these proteins generally consist of about 45 to 50 amino-acid residues. As shown in the following schematic representation, these peptides contain eight conserved cysteines involved in disulfide bonds.

+-------------------------------------------+
| +-------------------+ |
| | | |
xxCxxxxxxxxxxCxxxxxCxxxCxxxxxxxxxCxxxxxxCxCxxxC
| | | |
+---|----------------+ |
+------------------+

'C': conserved cysteine involved in a disulfide bond.

The folded structure of Gamma-purothionin is characterised by a well-defined 3-stranded anti-parallel beta-sheet and a short alpha-helix. Three disulfide bridges are located in the hydrophobic core between the helix and sheet, forming a cysteine-stabilised alpha-helical motif. This structure differs from that of the plant alpha- and beta-thionins, but is analogous to scorpion toxin

Scorpion toxin

Scorpion toxins are proteins found in the venom of scorpions. Their toxic effect may be mammal or insect specific, and acts by binding to sodium channels, inhibiting the inactivation of activated channels and blocking neuronal transmission....

s and insect defensin

Arthropod defensin

Arthropod defensins are a family of insect and scorpion cysteine-rich antibacterial peptides, primarily active against Gram-positive bacteria. All these peptides range in length from 38 to 51 amino acids...

s.

Databases

A database for antimicrobial peptides, including defensins is available: PhytAMP (http://phytamp.pfba-lab.org).

Subfamilies

• Gamma Purothionin