HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

J. Biol. Chem., Vol. 280, Issue 46, 38193-38202, November 18, 2005

This Article Full Text Full Text (PDF) All Versions of this Article: 280/46/38193    most recent M504200200v1 Submit a Letter to Editor Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Oberdorf, J. Articles by Skach, W. R. Search for Related Content PubMed PubMed Citation Articles by Oberdorf, J. Articles by Skach, W. R. Social Bookmarking                      What's this?

An Energy-dependent Maturation Step Is Required for Release of the Cystic Fibrosis Transmembrane Conductance Regulator from Early Endoplasmic Reticulum Biosynthetic Machinery^*

From the Department of Biochemistry and Moleculor Biology, Oregon Health & Sciences University, Portland, Oregon 97239

Polytopic proteins are synthesized in the endoplasmic reticulum (ER) by ribosomes docked at the Sec61 translocation channel. It is generally assumed that, upon termination of translation, polypeptides are spontaneously released into the ER membrane where final stages of folding and assembly are completed. Here we investigate early interactions between the ribosome-translocon complex and cystic fibrosis transmembrane conductance regulator (CFTR), a multidomain ABC transporter, and demonstrate that this is not always the case. Using in vitro and Xenopus oocyte expression systems we show that, during and immediately following synthesis, nascent CFTR polypeptides associate with large, heterogeneous, and dynamic protein complexes. Partial-length precursors were quantitatively isolated in a non-covalent, puromycin-sensitive complex (>3,500 kDa) that contained the Sec61 ER translocation machinery and the cytosolic chaperone Hsc70. Following the completion of synthesis, CFTR was gradually released into a smaller (600–800 kDa) ATP-sensitive complex. Surprisingly, release of full-length CFTR from the ribosome and translocon was significantly delayed after translation was completed. Moreover, this step required both nucleotide triphosphates and cytosol. Release of control proteins varied depending on their size and domain complexity. These studies thus identify a novel energy-dependent step early in the CFTR maturation pathway that is required to disengage nascent CFTR from ER biosynthetic machinery. We propose that, contrary to current models, the final stage of membrane integration is a regulated process that can be influenced by the state of nascent chain folding, and we speculate that this step is influenced by the complex multidomain structure of CFTR.

Received for publication, April 18, 2005 , and in revised form, September 8, 2005.

^* This work was supported by the Cystic Fibrosis Foundation Therapeutics Inc. and by National Institutes of Health Grants DK51818 and GM53457 (to W. R. S.) and T32 DK07674 (to J. O.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ Present address: Division of Hematology and Oncology, Portland Veterans Administration Medical Center, Portland, OR 97239.

² Present address: Dept. of Physiology and Pharmacology, Oregon Health & Sciences University, Portland, OR.

³ To whom correspondence should be addressed: Dept. of Biochemistry and Molecular Biology, Mail code L-224, Oregon Health & Sciences University, 3181 SW Sam Jackson Park Road, Portland, OR 97239. Tel.: 503-494-7322; Fax: 503-494-7368; E-mail: skachw{at}ohsu.edu.

CiteULike    Complore    Connotea    Del.icio.us    Digg    Reddit    Technorati    What's this?

This article has been cited by other articles:

				K. Du and G. L. Lukacs Cooperative Assembly and Misfolding of CFTR Domains In Vivo Mol. Biol. Cell, April 1, 2009; 20(7): 1903 - 1915. [Abstract] [Full Text] [PDF]

				D. Pitonzo, Z. Yang, Y. Matsumura, A. E. Johnson, and W. R. Skach Sequence-specific Retention and Regulated Integration of a Nascent Membrane Protein by the Endoplasmic Reticulum Sec61 Translocon Mol. Biol. Cell, January 1, 2009; 20(2): 685 - 698. [Abstract] [Full Text] [PDF]

				C. I. Popescu, A. Mares, L. Zdrentu, N. Zitzmann, R. A. Dwek, and S. M. Petrescu Productive Folding of Tyrosinase Ectodomain Is Controlled by the Transmembrane Anchor J. Biol. Chem., August 4, 2006; 281(31): 21682 - 21689. [Abstract] [Full Text] [PDF]