Purification and Characterization of Chaperonin 60 and Heat-Shock Protein 70 from Chromoplasts of Narcissus pseudonarcissus (Involvement of Heat-Shock Protein 70 in a Soluble Protein Complex Containing Phytoene Desaturase)

In chromoplast differentiation during flower formation in Narcissus pseudonarcissus, the molecular chaperones chaperonin 60 (Cpn60; α- and [beta]) and heat-shock protein 70 (Hsp70) greatly increase in abundance. Both were purified and shown to be present in a functional form in chromoplasts, indicating their requirement in the extensive structural rearrangements during the chloroplast-to-chromoplast transition. The purified proteins, sequenced N terminally and from internal peptides, showed strong homology to plastid Cpn60 and Hsp70 representatives from other plant species. During chromoplast differentiation, the carotenoid biosynthetic pathway is strongly induced. The corresponding enzymes are all nuclear encoded and form a large, soluble, hetero-oligomeric protein complex after import but prior to their membrane attachment. By immunoprecipitations we have shown that the plastid Hsp70 is a structural constituent of a soluble entity also containing phytoene desaturase.