XVI International Botanical Congess

We describe the cloning and in vitro reconstitution of phytochelatin (PC) synthase from Arabidopsis. The gene concerned, AtPCS1, encodes a 55 kDa polypeptide which when purified to homogeneity is sufficient for cadmium-activated synthesis of PCs containing 2, 3 and 4 Glu-Cys repeats from GSH in vitro. AtPCS1 binds cadmium stoichiometrically at high-affinity and is subject to a two-step activation cycle wherein reductant increases the accessibility of the metalloactivation domain while GSH binding to another site increases the affinity with which metal is bound. Since homologs of AtPCS1 are evident not only in the genome of S. pombe but also in that of C. elegans, the mechanistic analyses being undertaken on AtPCS1 will likely establish principles of broad applicability.