Abstract
Chloroplasts import more than 90% of their protein constituents from the cytosol. The import is mediated by translocon complexes located in the chloroplast envelope and the stroma. This review focuses on the two GTPases in the Toc (translocon at the outer envelope membrane of chloroplasts) complex. Hypotheses are presented about gating across the outer membrane and the possible functional states of the GTPases.
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References
Soll J., Schleiff E., Protein import into chloroplasts. Nat. Rev. Mol. Cell Biol. 5: 198–208, 2004
Kessler F., Schnell D.J., The function and diversity of plastid protein import pathways: a multilane GTPase highway into plastids. Traffic 7: 248–257, 2006
Chou M.-L., Chu C.-C., Chen L.-J., Akita M., Li H.-m., Stimulation of transit-peptide release and ATP hydrolysis by a cochaperone during protein import into chloroplasts. J. Cell Biol. 175: 893–900, 2006
Schleiff E., Soll J., Küchler M., Kühlbrandt W., Harrer R., Characterization of the translocon of the outer envelope of chloroplasts. J. Cell Biol. 160: 541–551, 2003
Hinnah S.C., Wagner R., Sveshnikova N., Harrer R., Soll J., The chloroplast protein import channel Toc75: pore properties and interaction with transit peptides. Biophy. J. 83: 899–911, 2002
Young M.E., Keegstra K., Froehlich J.E., GTP promotes the formation of early-import intermediates but is not required during the translocation step of protein import into chloroplasts. Plant Physiol. 121: 237–243, 1999
Kessler F., Blobel G., Patel H.A., Schnell D.J., Identification of two GTP-binding proteins in the chloroplast protein import machinery. Science 266: 1035–1039, 1994
Chen K., Chen X., Schnell D.J., Initial binding of preproteins involving the Toc159 receptor can be bypassed during protein import into chloroplasts. Plant Physiol. 122: 813–822, 2000
Schleiff E., Jelic M., Soll J., A GTP-driven motor moves proteins across the outer envelope of chloroplasts. Proc. Natl. Acad. Sci. USA 100: 4604–4609, 2003
Kessler F., Schnell D.J., Chloroplast protein import: solve the GTPase riddle for entry. Trends Cell Biol. 14: 334–338, 2004
Hiltbrunner A., Bauer J., Vidi P.-A., Infanger S., Weibel P., Hohwy M., Kessler F., Targeting of an abundant cytosolic form of the protein import receptor atToc159 to the outer chloroplast membrane. J. Cell Biol. 154: 309–316, 2001
Sun Y.-J., Forouhar F., Li H.-m., Tu S.-L., Yeh Y.-H., Kao S., Shr H.-L., Chou C.-C., Chen C., Hsiao C.-D., Crystal structure of pea Toc34, a novel GTPase of the chloroplast protein translocon. Nature Struc. Biol. 9: 95–100, 2002
Weibel P., Hiltbrunner A., Brand L., Kessler F., Dimerization of Toc-GTPases at the chloroplast protein import machinery. J. Biol. Chem. 278: 37321–37329, 2003
Flügge U., Benz R., Pore-forming activity in the outer membrane of the chloroplast envelope. FEBS Lett. 169: 85–89, 1984
Becker T., Jelic M., Vojta A., Radunz A., Soll J., Schleiff E., Preprotein recognition by the Toc complex. EMBO J 23: 520–530, 2004
Smith M.D., Hiltbrunner A., Kessler F., Schnell D.J., The targeting of the atToc159 preprotein receptor to the chloroplast outer membrane is mediated by its GTPase domain and is regulated by GTP. J. Cell Biol. 159: 833–843, 2002
Bauer J., Hiltbrunner A., Weibel P., Vidi P.-A., Alvarez-Huerta M., Smith M.D., Schnell D.J., Kessler F., Essential role of the G-domain in targeting of the protein import receptor atToc159 to the chloroplast outer membrane. J. Cell Biol. 159: 845–854, 2002
Wallas T., Smith M., Sanchez-Nieto S., Schnell D., The roles of Toc34 and Toc75 in targeting the Toc159 preprotein receptor to chloroplasts. J. Biol. Chem. 278: 44289–44297, 2003
Smith M., Rounds C., Wang F., Chen K., Afitlhile M., Schnell D., The cytoplasmic form of atToc159 is a selective transit peptide receptor for the import of nucleus-encoded chloroplast proteins. J. Cell Biol. 165: 323–334, 2004
Sveshnikova N., Soll J., Schleiff E., Toc34 is a preprotein receptor regulated by GTP and phosphorylation. Proc. Natl. Acad. Sci. USA 97: 4973–4978, 2000
Schleiff E., Soll J., Sveshnikova N., Tien R., Wright S., Dabney-Smith C., Subramanian C., Bruce B.D., Structural and guanosine triphosphate/diphosphate requirements for transit peptide recognition by the cytosolic domain of the chloroplast outer envelope receptor, Toc34. Biochemistry 41: 1934–1946, 2002
Jelic M., Soll J., Schleiff E., Two Toc34 homologues with different properties. Biochemistry 42: 5906–5916, 2003
Jelic M., Sveshnikova N., Motzkus M., Hörth P., Soll J., Schleiff E., The chloroplast import receptor Toc34 functions as preprotein-regulated GTPase. Biol. Chem. 383: 1875–1883, 2002
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This article is for the Special Issue of IMB 20th anniversary.
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Li, Hm., Kesavulu, M.M., Su, PH. et al. Toc GTPases. J Biomed Sci 14, 505–508 (2007). https://doi.org/10.1007/s11373-007-9166-2
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DOI: https://doi.org/10.1007/s11373-007-9166-2