Design, expression and characterisation of lysine-rich forms of the barley seed protein CI-2.

Chymotrypsin inhibitor CI-2 is a small (84 residue) barley seed protein that has been used extensively to study protein folding. It also contains eight lysine residues, making it an attractive target for expression in transgenic plants to increase their lysine contents. We have designed three lysine-enriched forms of CI-2 and compared their structures and properties with that of the wild type protein. One mutant containing three additional lysine residues in the inhibitory loop shows high stability to denaturation and reduced inhibitory activity, indicating its suitability for use in genetic engineering.