Functional Interaction of Chloroplast SRP/FtsY with the ALB3 Translocase in Thylakoids: Substrate Not Required

Integration of thylakoid proteins by the chloroplast signal recognition particle (cpSRP) posttranslational transport pathway requires the cpSRP, an SRP receptor homologue (cpFtsY), and the membrane protein ALB3. Similarly, Escherichia coli uses an SRP and FtsY to cotranslationally target membrane pr...

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Bibliographic Details
Published in:The Journal of cell biology 2003-09, Vol.162 (7), p.1245-1254
Main Authors: Moore, Misty, Goforth, Robyn L., Mori, Hiroki, Henry, Ralph
Format: Article
Language:English
Subjects:
Antibodies
Arabidopsis
Arabidopsis Proteins - metabolism
Bacteria
Bacterial Proteins - genetics
Bacterial Proteins - metabolism
Cellular biology
Chemical precipitation
Chloroplast Proteins
Chloroplasts
Chloroplasts - enzymology
Clines
Gels
Membrane proteins
Membranes
P branes
Protein transport
Proteins
Receptors
Receptors, Cytoplasmic and Nuclear - genetics
Receptors, Cytoplasmic and Nuclear - metabolism
Signal Recognition Particle - genetics
Signal Recognition Particle - metabolism
Substrate Specificity
Thylakoids
Thylakoids - enzymology
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Summary:Integration of thylakoid proteins by the chloroplast signal recognition particle (cpSRP) posttranslational transport pathway requires the cpSRP, an SRP receptor homologue (cpFtsY), and the membrane protein ALB3. Similarly, Escherichia coli uses an SRP and FtsY to cotranslationally target membrane proteins to the SecYEG translocase, which contains an ALB3 homologue, YidC. In neither system are the interactions between soluble and membrane components well understood. We show that complexes containing cpSRP, cpFtsY, and ALB3 can be precipitated using affinity tags on cpSRP or cpFtsY. Stabilization of this complex with GMP-PNP specifically blocks subsequent integration of substrate (light harvesting chl a/b-binding protein [LHCP]), indicating that the complex occupies functional ALB3 translocation sites. Surprisingly, neither substrate nor cpSRP43, a component of cpSRP, was necessary to form a complex with ALB3. Complexes also contained cpSecY, but its removal did not inhibit ALB3 function. Furthermore, antibody bound to ALB3 prevented ALB3 association with cpSRP and cpFtsY and inhibited LHCP integration suggesting that a complex containing cpSRP, cpFtsY, and ALB3 must form for proper LHCP integration.
ISSN:0021-9525
1540-8140
DOI:10.1083/jcb.200307067