Int J Biochem Mol Biol 2011;2(2):99-110

Original Article
A possible degree of motional freedom in bacterial chemoreceptor cytoplasmic domains
and its potential role in signal transduction

Weiguo Hu

Department of Polymer Science and Engineering, University of Massachusetts Amherst, MA 01003, USA.

Received January 31, 2011; accepted February 14, 2011; Epub February 25, 2011; published April 30, 2011

Abstract: We describe an array of gaps in an antiparallel four-helix bundle structure, the cytoplasmic domains of bacterial chemoreceptors.  
For a given helix, the side chain interactions that define a helix’s position are analyzed in terms of residue interfaces, the most important of
which are a-a, g-g, d-d, g-d, and a-d.  It was found that the interdigitation of the side groups does not entirely fill the space along the long axis of
the structure, which results in a rather regular array of gaps.  A simulated piston motion of helix CD1 along the helical axis direction by 1.2Å
shows that 85% of the side chain interactions still satisfy Van der Waals criteria, while the remaining clashes could be avoided by small
rotations of side chains.  Therefore, two states could exist in the structure, related by a piston motion.  Analysis of the crystal structure of a small
four-helix bundle, the P1short domain of CheA in Thermotoga Maritima, reveals that the two coexisting states related by a 1.3-1.7Å piston
motion are defined by the same mechanism.  This two-state model is a plausible candidate mechanism for the long distance signal
transduction in bacterial chemoreceptors and is qualitatively consistent with literature chemoreceptor mutagenesis results.  Such a
mechanism could exist in many other structures with interdigitating alpha-helices. (IJBMB1011005).

Keywords: Four-helix bundle, chemoreceptors, dynamics, signal transduction

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Weiguo Hu, PhD
Department of Polymer Science and Engineering
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University of Massachusetts Amherst, MA 01003
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