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J. Biol. Chem., Vol. 281, Issue 41, 30512-30523, October 13, 2006

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Competitive and Cooperative Interactions in Receptor Signaling Complexes^*

From the Department of Chemistry, the University of Massachusetts, Amherst, Massachusetts 01003

In bacterial chemotaxis, clustered transmembrane receptors and the adaptor protein CheW regulate the kinase CheA. Receptors outnumber CheA, yet it is poorly understood how interactions among receptors contribute to regulation. To address this problem, receptor clusters were simulated using liposomes decorated with the cytoplasmic domains of receptors, which supported CheA binding and stimulation. Competitive and cooperative interactions were revealed through the use of known receptor signaling mutants, which were used in mixtures with the wild type domain. Competitive effects among the receptor domains sorted cleanly into two categories defined by either stronger or weaker interactions with CheA. Cooperative effects were also evident in CheA binding and activity. In the transition from the stimulating to the inhibiting states, both the cooperativity of the transition and the persistence of stimulation by the wild type domain increased with receptor modification, as in the intact receptor. We conclude that competitive and cooperative receptor interactions both contribute to CheA regulation and that liposome-mediated assembly is effective in addressing these general membrane phenomena.

Received for publication, June 30, 2006 , and in revised form, August 9, 2006.

^* This work was supported in part by NIGMS Grant 5R01GM053210 from the National Institutes of Health and National Science Foundation Grant ACT/SGER CHE0346419 (to R. M. W.). 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 Equations S1–S13, supplemental Table S1, and supplemental Fig. S1.

¹ Recipient of a University of Massachusetts Amherst fellowship administered by National Institutes of Health-sponsored Chemistry-Biology Interface Training Program Grant 5T32GM008515.

² To whom correspondence should be addressed: Dept. of Chemistry, LGRT 701, 710 North Pleasant St., University of Massachusetts, Amherst, MA 01003-9336. Tel.: 413-545-0464; E-mail: rmweis{at}chem.umass.edu.

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