Two distinct translocation intermediates can be distinguished during protein transport by the TAT (Δph) pathway across the thylakoid membrane

During thylakoid transport of the chimeric precursor protein 16/23 which takes place by the twin arginine translocation (TAT) (Deltaph)-dependent pathway, two distinct translocation intermediates can be identified which represent successive steps in the translocation process. Both intermediates are partially inserted into the thylakoid membrane and can be distinguished by specific degradation fragments occurring after thermolysin treatment of the thylakoids. While the formation of the early translocation intermediate does not depend on a functional TAT translocation machinery, the appearance of the late intermediate is strictly coupled to the Deltaph-dependent transport of the 16/23 chimera. Accordingly, this translocation intermediate is found associated with two distinct complexes in the thylakoid membrane having apparent molecular masses of approximately 560 and 620 kDa, respectively.