NMR Solution Conformations and Interactions of Integrin αLβ2 Cytoplasmic Tails*
- School of Biological Sciences, Nanyang Technological University, 60 Nanyang Drive, Singapore 637551, Singapore
- 2 To whom correspondence may be addressed. Fax: 65-6791-3856; E-mail: smtan{at}ntu.edu.sg.
- 3 To whom correspondence may be addressed. Fax: 65-6791-3856; E-mail: surajit{at}ntu.edu.sg.
Abstract
The integrins are bi-directional signal transducers. Devoid of enzymatic activity, the integrin cytoplasmic tail serves as a hub for the recruitment of cytosolic proteins, and many of these are signaling molecules. The leukocyte-restricted integrin αLβ2 is essential for the adhesion, migration, and proliferation of leukocytes. Here we report solution conformations and interactions of the αLβ2 cytoplasmic tails by NMR analyses. The αL tail is characterized by three helical segments in the order of helix 1-3 that are connected by two loops with helix 3 having a number of nuclear Overhauser effect contacts with helix 1 and helix 2. The conformation of the β2 tail is less defined with only a helical segment restricted at its N terminus. Acidic residues from the helix 2-loop-helix 3 motif of αL were found to be responsible for its binding to calcium ion. There were detectable interactions between αL and β2 tails, involving helix 1 and helix 3 of the αL tail and the N-terminal helix of the β2 tail. Talin head domain that contains the FERM domain showed binding affinity of Kd ∼ 0.5 μm with the β2 tail. The binding affinity of αL and β2 tails is Kd ∼ 2.63 μm. These data are in line with the activating property of talin head domain on αLβ2 by which binding of talin head domain to β2 tail disrupts the interface of the αL and β2 tails that constrains αLβ2 in a resting state.
Footnotes
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↵4 The abbreviations used are: KSI, ketosteroid isomerase; CNBr, cyanogen bromide; HSQC, heteronuclear single quantum coherence; NOE, nuclear Overhauser effect; TCEP, tris(2-carboxyethyl) phosphine; NOESY, nuclear Overhauser effect spectroscopy; HPLC, high pressure liquid chromatography; ITC, isothermal titration calorimetry.
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The atomic coordinates and structure factors (code 2K8O) have been deposited in the Protein Data Bank, Research Collaboratory for Structural Bioinformatics, Rutgers University, New Brunswick, NJ (http://www.rcsb.org/).
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↵* This work was supported by Grants A*STAR BMRC 04/1/22/19/358 and 06/1/22/19/445 (to X.-Y. T., and S. M. T.) and by Grant A*STAR BMRC 06/01/22/19/446 (to A. B., H. M., and S. B.). 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.
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The on-line version of this article (available at http://www.jbc.org) contains supplemental Fig. 1.
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↵1 Both authors contributed equally to this work.
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- Received September 18, 2008.
- Revision received December 3, 2008.
- The American Society for Biochemistry and Molecular Biology, Inc.
