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Biophys. J. BioFAST: First Published January 28, 2005. doi:10.1529/biophysj.103.039321
© 2005 by the Biophysical Society.

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BIOPHYSICAL THEORY AND MODELING

G protein Coupled Enzyme Cascades have Intrinsic Properties that Improve Signal Localization and Fidelity

Sharad Ramanathan 1, Peter B. Detwiler 2, Anirvan M. Sengupta 3 and Boris I. Shraiman 3*

1 Bell Laboratories, Lucent Technologies, Murray Hill, NJ 07974
2 Dept of Physiology and Biophysics, University of Washington, Seattle,WA 98195.
3 Rutgers University

* To whom correspondence should be addressed. E-mail: shraiman{at}physics.rutgers.edu.

Submitted on December 30, 2003
Revised on May 3, 2004
Accepted on 8 October 2004


  Abstract
G protein coupled enzyme cascades are used by eukaryotic cells to detect external signals and transduce them into intracellular messages that contain biological information relevant to the cell's function. Since G protein coupled receptors that are designed to detect different kinds of external signals can generate the same kind of intracellular response, effective signaling requires that there are mechanisms to increase signal specificity and fidelity. Here we examine the kinetic equations for the initial three stages in a generic G protein coupled cascade and show that the physical properties of the transduction pathway result in two intrinsic features that benefit signaling. 1) The response to a single activated receptor is naturally confined to a localized signaling domain, which could improve signal specificity by reducing cross talk. 2) The peak of the response generated by such a signaling domain is limited. This saturation effect reduces trail-to-trail variability and increases signaling fidelity by limiting the response to receptors that remain active for longer than average. We suggest that this mechanism for reducing response fluctuations may be a contributing factor in making the single photon responses of vertebrate retinal rods so remarkably reproducible.

Key Words: G-protein, modeling, phototransduction




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Copyright © 2005 by the Biophysical Society.