Bringing BOS to light: Uncovering the key enzyme in the biosynthesis of the neurotoxin β-ODAP in Grass Pea (Lathyrus sativus L.)

Grass pea (Lathyrus sativus L.) is a grain legume commonly grown in parts of Asia and Africa for food and forage. While being a highly nutritious and robust crop, able to survive both drought and floods, it produces a neurotoxic compound, {beta}-N-oxalyl-L-,{beta}-diaminopropionic acid ({beta}-ODAP), which can cause a severe neurological disorder if consumed as a main diet component. So far, the enzyme that catalyzes the formation of {beta}-ODAP has not been identified. By combining protein purification and enzymatic assays with transcriptomic and proteomic analyses, we were able to identify the enzyme {beta}-ODAP synthetase (BOS) from grass pea. We show that BOS is an HXXXD-type acyltransferase of the BAHD superfamily and that its crystal structure is highly similar to that of plant hydroxycinnamoyl transferases. The identification of BOS, more than 50 years after it was proposed, paves the way towards the generation of non-toxic grass pea cultivars safe for human and animal consumption.