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J. Biol. Chem., Vol. 280, Issue 49, 40723-40730, December 9, 2005

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The Nanomechanics of Polycystin-1 Extracellular Region^*

Feng Qian, Wen Wei, Gregory Germino, and Andres Oberhauser1

From the Division of Nephrology, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205 and the Department of Neuroscience and Cell Biology and the Sealy Center for Structural Biology, University of Texas Medical Branch, Galveston, Texas 77555

Recent evidence suggests that polycystin-1 (PC1) acts as a mechanosensor, receiving signals from the primary cilia, neighboring cells, and extracellular matrix and transduces them into cellular responses that regulate proliferation, adhesion, and differentiation that are essential for the control of renal tubules and kidney morphogenesis. PC1 has an unusually long extracellular region (3000 amino acids) with a multimodular structure. Proteins with a similar architecture have structural and mechanical roles. Based on the structural similarities between PC1 and other modular proteins that have elastic properties we hypothesized that PC1 functions mechanically by providing a flexible and elastic linkage between cells. Here we directly tested this hypothesis by analyzing the mechanical properties of the entire PC1 extracellular region by using single molecule force spectroscopy. We show that the PC1 extracellular region is highly extensible and that this extensibility is mainly caused by the unfolding of its Ig-like domains. Stretching the native PC1 extracellular region results in a sawtooth pattern with equally spaced force peaks that have a wide range of unfolding forces (50-200 pN). By combining single-molecule force spectroscopy and protein engineering techniques, we demonstrate that the sawtooth pattern in native PC1 extracellular region corresponds to the sequential unfolding of individual Ig-like domains. We found that Ig-like domains refold after mechanical unfolding. Hence, the PC1 extracellular region displays a dynamic extensibility whereby the resting length might be regulated through unfolding/refolding of its Ig-like domains. These force-driven reactions may be important for cell elasticity and the regulation of cell signaling events mediated by PC1.

Received for publication, September 1, 2005 , and in revised form, October 7, 2005.

^* This work was supported by grants from the National Institutes of Health (DK067443, to A. O.; DK062199, to F. Q.; and DK48006, DK57325, to G. G.), the American Heart Association (to F. Q.), and the John Sealy Memorial Endowment Fund (to A. 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 To whom correspondence should be addressed: Dept. of Neuroscience and Cell Biology, and Sealy Center for Structural Biology, University of Texas Medical Branch, Galveston, TX 77555-0437. Tel.: 409-772-1309; Fax: 409-772-1301; E-mail: afoberha{at}utmb.edu.

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