The Journal of Cell Biology, Vol 111, 1825-1838, Copyright © 1990 by The Rockefeller University Press

ARTICLES

The chloroplast import receptor is an integral membrane protein of chloroplast envelope contact sites

DJ Schnell, G Blobel and D Pain
Laboratory of Cell Biology, Howard Hughes Medical Institute, Rockefeller University, New York, New York 10021.

A chloroplast import receptor from pea, previously identified by antiidiotypic antibodies was purified and its primary structure deduced from its cDNA sequence. The protein is a 36-kD integral membrane protein (p36) with eight potential transmembrane segments. Fab prepared from monospecific anti-p36 IgG inhibits the import of the ribulose-1,5- bisphosphate carboxylase small subunit precursor (pS) by interfering with pS binding at the chloroplast surface. Anti-p36 IgGs are able to immunoprecipitate a Triton X-100 soluble p36-pS complex, suggesting a direct interaction between p36 and pS. This immunoprecipitation was specific as it was abolished by a pS synthetic transit peptide, consistent with the transit sequence receptor function of p36. Immunoelectron microscopy localized p36 to regions of the outer chloroplast membrane that are in close contact with the inner chloroplast membrane. Comparison of the deduced sequence of pea p36 to that of other known proteins indicates a striking homology to a protein from spinach chloroplasts that was previously suggested to be the triose phosphate-3-phosphoglycerate-phosphate translocator (phosphate translocator) (Flugge, U. I., K. Fischer, A. Gross, W. Sebald, F. Lottspeich, and C. Eckerskorn. 1989. EMBO (Eur. Mol. Biol. Organ.) J. 8:39-46). However, incubation of Triton X-100 solubilized chloroplast envelope material with hydroxylapatite indicated that p36 was quantitatively absorbed, whereas previous reports have shown that phosphate translocator activity does not bind to hydroxylapatite (Flugge, U. I., and H. W. Heldt. 1981. Biochim. Biophys. Acta. 638:296- 304. These data, in addition to the topology and import inhibition data presented in this report support the assignment of p36 as a receptor for chloroplast protein import, and argue against the assignment of the spinach homologue of this protein as the chloroplast phosphate translocator.
CiteULike    Complore    Connotea    Del.icio.us    Digg    Facebook    Reddit    Technorati    Twitter    What's this?

This article has been cited by other articles:

• Wang, Q., Sullivan, R. W., Kight, A., Henry, R. L., Huang, J., Jones, A. M., Korth, K. L. (2004). Deletion of the Chloroplast-Localized Thylakoid Formation1 Gene Product in Arabidopsis Leads to Deficient Thylakoid Formation and Variegated Leaves. Plant Physiol. 136: 3594-3604 [Abstract] [Full Text]  
• Hirohashi, T., Hase, T., Nakai, M. (2001). Maize Non-Photosynthetic Ferredoxin Precursor Is Mis-Sorted to the Intermembrane Space of Chloroplasts in the Presence of Light. Plant Physiol. 125: 2154-2163 [Abstract] [Full Text]  
• Kouranov, A., Chen, X., Fuks, B., Schnell, D. J. (1998). Tic20 and Tic22 Are New Components of the Protein Import Apparatus at the Chloroplast Inner Envelope Membrane. JCB 143: 991-1002 [Abstract] [Full Text]  
• Walker, D., Chaddock, A. M., Chaddock, J. A., Roberts, L. M., Lord, J. M., Robinson, C. (1996). Ricin A Chain Fused to a Chloroplast-targeting Signal Is Unfolded on the Chloroplast Surface Prior to Import across the Envelope Membranes. J. Biol. Chem. 271: 4082-4085 [Abstract] [Full Text]  
• Ko, K., Budd, D., Wu, C., Seibert, F., Kourtz, L., Ko, Z. W. (1995). Isolation and Characterization of a cDNA Clone Encoding a Member of the Com44/Cim44 Envelope Components of the Chloroplast Protein Import Apparatus. J. Biol. Chem. 270: 28601-28608 [Abstract] [Full Text]  
• Creighton, A. M., Hulford, A., Mant, A., Robinson, D., Robinson, C. (1995). A Monomeric, Tightly Folded Stromal Intermediate on the DeltapH-dependent Thylakoidal Protein Transport Pathway. J. Biol. Chem. 270: 1663-1669 [Abstract] [Full Text]  
• Hirsch, S, Muckel, E, Heemeyer, F, von Heijne, G, Soll, J (1994). A receptor component of the chloroplast protein translocation machinery. Science 266: 1989-1992 [Abstract]  
• Schnell, D., Kessler, F, Blobel, G (1994). Isolation of components of the chloroplast protein import machinery. Science 266: 1007-1012 [Abstract]  

Home | Help | Feedback | Subscriptions | Archive | Search | Table of Contents