Isolation of the epithiospecifier protein from oil-rape (Brassica napus ssp. oleifera) seed and its characterization

The epithiospecifier protein (ESP) is a myrosinase (MYR) cofactor, which is necessary to drive the MYR-catalyzed hydrolysis of some specific glucosinolates towards the production of cyanoepithioalkanes instead of isothiocyanates and nitriles. ESP was isolated from Brassica napus seeds by anionic exchange and gel filtration chromatography. ESP showed a molecular weight of about 39 kDa and pI 5.3. The amino acid sequence of several tryptic peptides of ESP (accounting for about 50% of the total sequence) made it possible to establish the high similarity (81% identity) with a hypothetical 37 kDa protein (TrEMBL data base accession number Q39104) and several jasmonate-inducible proteins from Arabidopsis thaliana. This observation suggests that ESP is likely to be involved in jasmonate-mediated defence and disease resistance mechanisms.