The importance of the C-terminal region and Cys residues for the membrane association of the NADPH:protochlorophyllide oxidoreductase in pea

In vitro chloroplast import reactions and thylakoid association reactions have been performed with a series of C-terminal deletions and Cys-to-Ser substitution mutants of the pea NADPH:protochlorophyllide oxidoreductase (POR; EC 1.6.99). C-terminal deletions of the precursor POR (Delta 362-400, Delta 338-400, Delta 315-400 and Delta 300-400) were efficiently translocated across the chloroplast envelope. However, except the Delta 396-400 mutant, no C-terminal deletion mutants or Cys-to-Ser substitution (Cys119, Cys281 and Cys309) mutants resisted posttreatment with thermolysin after the thylakoid association reactions. This suggests that these mutants were unable to properly associate to the thylakoids due to changes of the protein conformation of POR. (C) 2001 Federation of European Biochemical Societies. Published by Elsevier Science B.V. All rights reserved.