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J. Biol. Chem., Vol. 281, Issue 42, 31638-31646, October 20, 2006

This Article Full Text Full Text (PDF) Supplemental Data All Versions of this Article: 281/42/31638    most recent M604770200v1 Alert me when this article is cited 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 Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Mueller, S. Articles by Paschke, R. Search for Related Content PubMed PubMed Citation Articles by Mueller, S. Articles by Paschke, R. Social Bookmarking                      What's this?

Significance of Ectodomain Cysteine Boxes 2 and 3 for the Activation Mechanism of the Thyroid-stimulating Hormone Receptor^*

Sandra Mueller¹, Gunnar Kleinau¹, Holger Jaeschke, Susanne Neumann^¶, Gerd Krause, and Ralf Paschke²

From the III Medical Department, University of Leipzig, Philipp-Rosenthal-Strasse 27, D-04103 Leipzig, Germany, Leibniz-Institut für Molekulare Pharmakologie, Robert-Roessle-Strasse 10, D-13125 Berlin, Germany, and ^¶NIDDK, National Institutes of Health, Clinical Endocrinology Branch, Bethesda, Maryland 20892

Recently, we identified constitutively activating mutations at positions Asp-403, Glu-404, and Asn-406 in the third extracellular cysteine box (C-b3) of the thyroid-stimulating hormone receptor. We hypothesized that this region could act as a molecular interface between the extracellular and serpentine domain. In this study we present a model for properties of potential interaction partners for this region. Moreover, we show that Pro-400 and Pro-407 adjacent to this epitope are also important for stabilizing the partially active, basal conformation of the wild-type (WT) thyroid-stimulating hormone receptor. Furthermore, the mutation K291A in the second extracellular cysteine box (C-b2) was identified as a new constitutively activating mutation that releases the basal conformation of the WT receptor like the known tryptic cleavage in its close vicinity. Taken together, we provide an activation scenario at the C-b2/C-b3 unit. Three anchor fragments (anchors I-III) most likely constrain the basal conformation. The three anchor fragments are tightly packed. A disulfide bridge holds the C-b2/C-b3 portions in close positions. Independent of the type of conformational interference such as side chain modifications, tryptic cleavage, or hormone stimulation that act on the constrained C-b2/C-b3 WT conformation, it will always release one of the anchor fragments. Subsequently, this results in a conformational displacement of the C-b2/C-b3 portions relative to each other, inducing receptor activation.

Received for publication, May 18, 2006 , and in revised form, July 14, 2006.

^* This work was supported by Deutsche Forschungsgemeinschaft Grants KR 1223/1-2 and PA 423 12-2 and by the Intramural Research Program of NIDDK, National Institutes of Health. 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.

The on-line version of this article (available at http://www.jbc.org) contains supplemental Table S1.

¹ Both authors contributed equally to this work.

² To whom correspondence should be addressed. Tel.: 49-341-9713200; Fax: 49-341-9713209; E-mail: pasr{at}medizin.uni-leipzig.de.

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