Ligand depletion in vivo modulates the dynamic range and cooperativity of signal transduction.

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TitleLigand depletion in vivo modulates the dynamic range and cooperativity of signal transduction.
Publication TypeJournal Article
Year of Publication2010
AuthorsEdelstein, SJ, Stefan, MI, Le Novère, N
JournalPLoS One
Volume5
Issue1
Paginatione8449
Date Published2010
ISSN1932-6203
KeywordsBacterial Proteins, Calmodulin, Escherichia coli, Ligands, Membrane Proteins, Protein Binding, Signal Transduction
Abstract

<p>Biological signal transduction commonly involves cooperative interactions in the binding of ligands to their receptors. In many cases, ligand concentrations in vivo are close to the value of the dissociation constant of their receptors, resulting in the phenomenon of ligand depletion. Using examples based on rotational bias of bacterial flagellar motors and calcium binding to mammalian calmodulin, we show that ligand depletion diminishes cooperativity and broadens the dynamic range of sensitivity to the signaling ligand. As a result, the same signal transducer responds to different ranges of signal with various degrees of cooperativity according to its effective cellular concentration. Hence, results from in vitro dose-response analyses cannot be applied directly to understand signaling in vivo. Moreover, the receptor concentration is revealed to be a key element in controlling signal transduction and we propose that its modulation constitutes a new way of controlling sensitivity to signals. In addition, through an analysis of the allosteric enzyme aspartate transcarbamylase, we demonstrate that the classical Hill coefficient is not appropriate for characterizing the change in conformational state upon ligand binding to an oligomeric protein (equivalent to a dose-response curve), because it ignores the cooperativity of the conformational change for the corresponding equivalent monomers, which are generally characterized by a Hill coefficient . Therefore, we propose a new index of cooperativity based on the comparison of the properties of oligomers and their equivalent monomers.</p>

DOI10.1371/journal.pone.0008449
Alternate JournalPLoS ONE
PubMed ID20052284
PubMed Central IDPMC2797075
Grant List / / Wellcome Trust / United Kingdom