Co-Translational Targeting of Leader Peptidase to the Thylakoid Membrane; Reconstitution in a Homologous Chloroplast Translation System

Chapter

Abstract

Very little is known about the mechanisms of targeting, insertion and assembly of the about 30 chloroplast-encoded thylakoid membrane proteins, despite their importance. Since chloroplasts are originally derived from prokaryotes, it can be postulated that targeting pathways of the chloroplast encoded proteins will show strong homology to those in E. coli.. Indeed several chloroplast homologues of E.coli targeting components have been identified such as SecA (1,2), SecY (3) as well as the 54 kDa subunit of the Signal Recognition Particle (SRP) (4). We decided to study the extent of conservation and mechanisms of the chloroplast targeting mechanisms by translating E.coli Leader peptidase (Lep) in a homologous chloroplast translation system (5) and to try to target Lep to the thylakoid membrane. Lep is an inner membrane protein with two membrane spans and has served as a model protein to study targeting and insertion to the E. coli inner membrane (6) as well as to ER membranes (e.g.7). Lep is made without a cleavable signal sequence and its N- and C-terminal domains face the periplasmic side of the inner membrane (Fig. 1). In E.coli targeting and insertion is a co-translational process and is SRP, SecA and SecY dependent (8–10). Targeting of Lep to the ER membrane also requires SRP and detailed in vitro studies indicated a co-translational insertion of Lep into the ER membrane (7).

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Copyright information

© Springer Science+Business Media Dordrecht 1998

Authors and Affiliations

  1. 1.Dept. of BiochemistryStockholm UniversityStockholmSweden

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