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Published 29 September 2003. doi:10.1083/jcb.200307067
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© The Rockefeller University Press, 0021-9525/2003/9/1245 $5.00
The Journal of Cell Biology, Volume 162, Number 7, 1245-1254

Article

 Functional interaction of chloroplast SRP/FtsY with the ALB3 translocase in thylakoids : substrate not required



Misty Moore1, Robyn L. Goforth1,2, Hiroki Mori3 and Ralph Henry1

1 Department of Biological Sciences, University of Arkansas, Fayetteville, AR 72701
2 Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, AR 72701
3 Graduate School of Natural Science and Technology, Okayama University, Okayama 700-8530 Japan

Address correspondence to Ralph Henry, Dept. of Biological Sciences, 601 Science Engineering Building, University of Arkansas, Fayetteville, AR 72701. Tel.: (479) 575-2529. Fax: (479) 575-4010. email: Ralph.Henry{at}uark.edu

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.

Key Words: protein transport; signal recognition particle; receptors; membrane proteins; Arabidopsis proteins

The online version of this article includes supplemental material.

Abbreviations used in this paper: chl, chlorophyll; cpSRP, chloroplast signal recognition particle; cpTAT, chloroplast twin-arginine translocation; GMP-PNP, 5'-guanylyl-imidodiphosphate trisodium salt; LHCP, light harvesting chl a/b-binding protein; OE, oxygen-evolving complex; SE, stromal extract; Sec, secretory; SPDP, N-succinimidyl 3-[2-pyridyldithio]-propionate.


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