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ATP-independent reversal of a membrane protein aggregate by a chloroplast SRP subunit

Nature Structural & Molecular Biology volume 17, pages 696–702 (2010)Cite this article

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Abstract

Membrane proteins impose enormous challenges to cellular protein homeostasis during their post-translational targeting, and they require chaperones to keep them soluble and translocation competent. Here we show that a novel targeting factor in the chloroplast signal recognition particle (cpSRP), cpSRP43, is a highly specific molecular chaperone that efficiently reverses the aggregation of its substrate proteins. In contrast to 'ATPases associated with various cellular activities' (AAA+) chaperones, cpSRP43 uses specific binding interactions with its substrate to mediate its 'disaggregase' activity. This disaggregase capability can allow targeting machineries to more effectively capture their protein substrates and emphasizes a close connection between protein folding and trafficking processes. Moreover, cpSRP43 provides the first example to our knowledge of an ATP-independent disaggregase and shows that efficient reversal of protein aggregation can be attained by specific binding interactions between a chaperone and its substrate.

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Figure 1: cpSRP43 prevents aggregation of LHCP.
Figure 2: LHCP binds cpSRP43 with high affinity.
Figure 3: cpSRP and cpSRP43 chaperone various members of the LHC family.
Figure 4: cpSRP43 actively reverses LHCP aggregation.
Figure 5: Specific binding interactions between LHCP and cpSRP43 are essential for chaperone activity.
Figure 6: Chromodomains are essential for cpSRP43's chaperone activity.
Figure 7: cpSRP43 or LHCP mutants defective in chaperone activity could not support LHCP targeting and translocation.
Figure 8: SAXS reconstruction of full-length cpSRP43.

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Acknowledgements

We thank R. Henry (Univ. of Arkansas) for expression plasmids of cpSRP43 and LHCP, C. Robinson (Univ. of Warwick) for plasmids encoding LHCA1 and LHCB5, Z. Liu for help and advice with LHCP reconstitution, A. Sim and V. Chu of the Doniach group and D. Herschlag for help and advice with the SAXS experiments and D.C. Rees, W.M. Clemons, A. Varshavsky, N. Pierce and members of the Shan laboratory for comments on the manuscript. This work was supported by US National Institutes of Health grant GM078024 and career awards from the Burroughs Welcome Foundation, the Henry and Camille Dreyfus foundation, the Beckman foundation and the Packard foundation to S.-o.S. and by US National Institutes of Health program project grant P01-GM-66275 to S.D. and D.H.

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  1. Kuang Shen and Vinh Q Lam: These authors contributed equally to this work.

Authors and Affiliations

  1. Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California, USA

    Peera Jaru-Ampornpan, Kuang Shen, Vinh Q Lam, Tony Z Jia & Shu-ou Shan

  2. Department of Physics and Applied Physics, Stanford University, Stanford, California, USA

    Mona Ali & Sebastian Doniach

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  1. Peera Jaru-Ampornpan
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Contributions

P. J.-A. and S.-o.S. designed experiments; P.J.-A. and T.Z.J. performed the biochemical experiments and analyzed data; V.Q.L. and M.A. performed the SAXS experiment and analyzed data; K.S., M.A. and S.D. carried out molecular dynamics simulations of SAXS data; P. J.-A. and S.-o.S. wrote the paper.

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Correspondence to Shu-ou Shan.

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Jaru-Ampornpan, P., Shen, K., Lam, V. et al. ATP-independent reversal of a membrane protein aggregate by a chloroplast SRP subunit. Nat Struct Mol Biol 17, 696–702 (2010). https://doi.org/10.1038/nsmb.1836

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