Purification of plant protein phosphatase PP7 and evidence for its redox regulation

PP7, a recently identified protein Ser/Thr phosphatase of the PPP family di stantly related to phosphatases PP5/PPT and PPEF/rdgC, was purified from ca uliflower extracts to apparent homogeneity. Purified cauliflower PP7 and re combinant PP7 expressed in Escherichia coli exhibit light absorption in the visible range with a maximum at similar to 430 nm. Under nonreducing condi tions, native PP7 exists as a mixture of monomer with an intramolecular dis ulfide bridge, disulfide-linked homodimer, and possibly disulfide-linked co mplexes with potential partner proteins. The activity of recombinant Arabid opsis thaliana PP7 is reversibly regulated by redox agents. The results dem onstrate the existence of PP7 protein in planta and suggest a possibility o f redox regulation of this protein phosphatase. (C) 2001 Elsevier Science.