MOLECULAR CHAPERONES AND PROTEIN-FOLDING IN PLANTS

Protein folding in vivo is mediated by an array of proteins that act e ither as 'foldases' or 'molecular chaperones'. Foldases include protei n disulfide isomerase and peptidyl prolyl isomerase, which catalyze th e rearrangement of disulfide bonds or isomerization of peptide bonds a round Pro residues, respectively. Molecular chaperones are a diverse g roup of proteins, but they share the property that they bind substrate proteins that are in unstable, non-native structural states. The best understood chaperone systems are HSP70/DnaK and HSP60/GroE, but consi derable data support a chaperone role for other proteins, including HS P100, HSP90, small HSPs and calnexin. Recent research indicates that m any, if not all, cellular proteins interact with chaperones and/or fol dases during their lifetime in the cell. Different chaperone and folda se systems are required for synthesis, targeting, maturation and degra dation of proteins in all cellular compartments. Thus, these diverse p roteins affect an exceptionally broad array of cellular processes requ ired for both normal cell function and survival of stress conditions. This review summarizes our current understanding of how these proteins function in plants, with a major focus on those systems where the mos t detailed mechanistic data are available, or where features of the ch aperone/foldase system or substrate proteins are unique to plants.