THE SECONDARY STRUCTURE OF THE FERREDOXIN TRANSIT SEQUENCE IS MODULATED BY ITS INTERACTION WITH NEGATIVELY CHARGED LIPIDS

Import of proteins into chloroplasts depends on an N-terminal transit sequence. Transit sequences contain little primary sequence similarity and therefore recognition of these sequences is thought to involve sp ecific folding. To assess the conformational flexibility of the transi t sequence, we studied the transit peptide of preferredoxin (trfd) by circular dichroism. In buffer, trfd is in a random coil conformation. A large increase in alpha-helix was induced in the presence of micelle s or vesicles formed by anionic lipids. Less pronounced changes in sec ondary structure were induced by zwitterionic detergents but no change s were observed in the presence of neutral detergents or vesicles comp osed of phosphatidylcholine.