Plant defensin

Plant defensins (Formerly gamma-thionins) are a family of small, cysteine-rich proteins found in plants that serve to defend them against parasites.

Contents

• Databases
• Subfamilies
• References

The following plant proteins belong to this family:

The flower-specific Nicotiana alata defensin (NaD1)

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 (Common Tobacco).

Antifungal proteins (AFP) from the seeds of Brassicaceae species such as radish, mustard, turnip and Arabidopsis thaliana (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 (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 toxins and insect defensins.