- Risor MW, Thomsen LR, Sanggaard KW, Nielsen TA, Thogersen IB, Lukassen MV, Rossen L, Garcia-Ferrer I, Guevara T, Scavenius C, Meinjohanns E, Gomis-Ruth FX, Enghild JJ
- Enzymatic and structural characterization of the major endopeptidase in the Venus flytrap digestion fluid.
- J Biol Chem. 2015 Dec 1. pii: jbc.M115.672550.
- Carnivorous plants primarily use aspartic proteases during digestion of captured prey. In contrast, the major endopeptidases in the digestive fluid of the Venus flytrap (Dionaea muscipula) are cysteine proteases (dionain-1 to -4). Here, we present the crystal structure of mature dionain-1 in covalent complex with inhibitor E-64 at 1.5 A resolution. The enzyme exhibits an overall protein fold reminiscent of other plant cysteine proteases. The inactive glycosylated pro-form undergoes autoprocessing and self-activation, optimally at the physiologically relevant pH value of 3.6, at which the protective effect of the pro-domain is lost. The mature enzyme was able to efficiently degrade a Drosophila fly protein extract at pH 4 showing high activity against the abundant Lys- and Arg-rich protein, myosin. The substrate specificity of dionain-1 was largely similar to that of papain with preference for hydrophobic and aliphatic residues in subsite S2 and for positively charged residues in S1. A tentative structure of the pro-domain was obtained by homology modeling and suggested that a pro-peptide Lys residue intrudes the S2 pocket which is more spacious than in papain. This study provides the first analysis of a cysteine protease from the digestive fluid of a carnivorous plant and confirms the close relationship between carnivorous action and plant defense mechanisms.