1.C.45 The Plant Defensin (Plant Defensin) Family
Plant defensins form ion channels capable of transporting H+, Ca2+ and K+. However a concentration as great as 10x above the toxic concentration may be required to demonstrate increased permeability. The mature peptides are about 45-54aas in length. They possess eight disulfide linked cysteines. They were initially called γ-thionins, but x-ray analyses revealed that thionins and plant defensins are structurally unrelated. Defensins are typified by a triple stranded antiparallel β-sheet plus one α-helix. The two cysteines in the CXXXC segment of the α-helix are connected to the two cysteines in the CXC segment of the C-terminal β-strand. They resemble insect defensins in fold except for the amino terminal β-strand of the plant defensins. The conserved residues include the 8 Cs, 2 Gs (at positions 13 and 34), an aromatic residue (at position 11), and an E (at position 29). Multiple plant defensin genes are found in a single plant genome.
The generalized transport reaction catalyzed by plant defensins is:
small molecules (in) ⇌ small molecules (out)
