IQ motif selectivity in human IQGAP1: binding of myosin essential light chain and S100B

  • Sevvel Pathmanathan
  • Sarah F. Elliott
  • Sara McSwiggen
  • Brett Greer
  • Pat Harriott
  • G. Brent Irvine
  • David J. Timson


IQGAPs are cytoskeletal scaffolding proteins which link signalling pathways to the reorganisation of actin and microtubules. Human IQGAP1 has four IQ motifs each of which binds to calmodulin. The same region has been implicated in binding to two calmodulin-like proteins, the myosin essential light chain Mlc1sa and the calcium and zinc ion binding protein S100B. Using synthetic peptides corresponding to the four IQ motifs of human IQGAP1, we showed by native gel electrophoresis that only the first IQ motif interacts with Mlc1sa. This IQ motif, and also the fourth, interacts with the budding yeast myosin essential light chain Mlc1p. The first and second IQ motifs interact with S100B in the presence of calcium ions. This clearly establishes that S100B can interact with its targets through IQ motifs in addition to interacting via previously reported sequences. These results are discussed in terms of the function of IQGAP1 and IQ motif recognition.


Calcium ions Cytoskeleton EF-hand IQ motif Mlc1sa Native gel 



Adenomatous polyposis coli




Fasciola hepatica type 2 calmodulin




2-(1H-7-azabenzotriazol-1-yl)-1,1,3,3-tetramethyl uronium hexafluorophosphate methanaminium

IQ1, IQ2, IQ3, IQ4

The first, second, third and fourth IQ motifs (as numbered from the N-terminus), respectively, of human IQGAP1


The apparent disassociation constant under the conditions of native gel electrophoresis




Trifluoroacetic acid


Vascular endothelial growth factor receptor



We thank Sean Russell for providing FhCaM2 protein which was used as a control in these experiments and Maelíosa Mc Crudden for preliminary work on the purification of Mlc1sa. This work was funded in part by a grant from the BBSRC (reference BB/D000394/1). Sevvel Pathmanathan gratefully acknowledges a studentship from Queen’s University, Belfast and the University of Jaffna (Sri Lanka) for giving him leave of absence to complete this work.


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Copyright information

© Springer Science+Business Media, LLC. 2008

Authors and Affiliations

  • Sevvel Pathmanathan
    • 1
  • Sarah F. Elliott
    • 1
  • Sara McSwiggen
    • 1
  • Brett Greer
    • 1
  • Pat Harriott
    • 1
  • G. Brent Irvine
    • 2
  • David J. Timson
    • 1
  1. 1.Medical Biology Centre, School of Biological SciencesQueen’s University BelfastBelfastUK
  2. 2.School of Medicine & DentistryQueen’s University BelfastBelfastUK

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