1.C.44 The Plant Thionin (PT) Family

Most mature plant thionins are 45-47aas in length, but their precursors are larger (70-80aas). There are two subgroups, the 8 cysteine (4 disulfide bridge) and the six cysteine (3 disulfide bridge) thionins. Thionin sequences are highly divergent, and only the six cysteines at positions 3, 4, 10, 27, 33 and 41 as well as an arginine at position 10 and an aromatic residue at position 13 are well conserved. Three-dimensional analyses reveal a very similar fold for all thionins (an L shape with the long arm formed by two antiparallel α-helices and the short arm by two antiparallel β-strands). There amphipathic structures inhibit the growth of bacteria and fungi. They form pores in the membranes of these cells as well as of yeast, animal cells and plant protoplasts. Ions transported include H⁺, Ca²⁺, K⁺, and H₂PO₄^-. Organic substances (amino acids, nucleobases, sugars) are also released via these channels.

The generalized transport reaction is:

small molecules (in) small molecules (out)