Structure of an allosteric inhibitor of LFA-1 bound to the I-domain studied by crystallography, NMR, and calorimetry.

Crump, Matthew P, Ceska, Thomas A, Spyracopoulos, Leo, Henry, Alistair, Archibald, Sarah C, Alexander, Rikki, Taylor, Richard J, Findlow, Stuart C. , O'Connell, James, Robinson, Martyn K and Shock, Anthony (2004) Structure of an allosteric inhibitor of LFA-1 bound to the I-domain studied by crystallography, NMR, and calorimetry. Biochemistry, 43, (9), 2394-2404.


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LFA-1 (lymphocyte function-associated antigen-1) plays a role in intercellular adhesion and lymphocyte trafficking and activation and is an attractive anti-inflammatory drug target. The alpha-subunit of LFA-1, in common with several other integrins, has an N-terminally inserted domain (I-domain) of approximately 200 amino acids that plays a central role in regulating ligand binding to LFA-1. An additional region, termed the I-domain allosteric site (IDAS), has been identified exclusively within the LFA-1 I-domain and shown to regulate the function of this protein. The IDAS is occupied by small molecule LFA-1 inhibitors when cocrystallized or analyzed by (15)N-(1)H HSQC (heteronuclear single-quantum coherence) NMR (nuclear magnetic resonance) titration experiments. We report here a novel arylthio inhibitor that binds the I-domain with a K(d) of 18.3 nM as determined by isothermal titration calorimetry (ITC). This value is in close agreement with the IC(50) (10.9 nM) derived from a biochemical competition assay (DELFIA) that measures the level of inhibition of binding of whole LFA-1 to its ligand, ICAM-1. Having established the strong affinity of the arylthio inhibitor for the isolated I-domain, we have used a range of techniques to further characterize the binding, including ITC, NMR, and X-ray crystallography. We have first developed an effective ITC binding assay for use with low-solubility inhibitors that avoids the need for ELISA-based assays. In addition, we utilized a fast NMR-based assay for the generation of I-domain-inhibitor models. This is based around the collection of HCCH-TOCSY spectra of LFA-1 in the bound form and the identification of a subset of side chain methyl groups that give chemical shift changes upon binding of LFA-1 inhibitors. This subset was used in two-dimensional (13)C-(15)N and (15)N-filtered and -edited two-dimensional NMR experiments to identify a minimal set of intraligand and ligand-protein NOEs, respectively (nuclear Overhauser enhancements). Models from the NMR data were assessed by comparison to an X-ray crystallographic structure of the complex, confirming that the method correctly predicted the essential features of the bound ligand.

Item Type: Article
ISSNs: 0006-2960 (print)
1520-4995 (electronic)
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Subjects: Q Science > Q Science (General)
Divisions: University Structure - Pre August 2011 > School of Biological Sciences
ePrint ID: 156683
Date Deposited: 01 Jun 2010 13:30
Last Modified: 27 Mar 2014 19:14

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