Characterization and regulation of an additional actin-filamentbinding site in large isoforms of the stereocilia actin-bundling protein espin

Lili Zheng, Dina M. Beeler, James R. Bartles*

*Corresponding author for this work

Research output: Contribution to journalArticle

15 Scopus citations


The espin actin-bundling proteins, which are produced as isoforms of different sizes from a single gene, are required for the growth of hair cell stereocilia. We have characterized an additional actinfilament- binding site present in the extended amino-termini of large espin isoforms. Constitutively active in espin 2, the site increased the size of actin bundles formed in vitro and inhibited actin fluorescence recovery in microvilli. In espin 1, which has an Nterminal ankyrin repeat domain, the site was autoinhibited by binding between the ankyrin repeat domain and a peptide near the actin-binding site. Deletion of this peptide from espin 1 activated its actin-binding site. The peptide resembled tail homology domain I of myosin III, a ligand of the ankyrin repeat domain localized with espin 1 at the tip of stereocilia. A myosin III tail homology domain I peptide, but not scrambled control peptides, inhibited internal binding of the ankyrin repeat domain and released the espin 1 actin-binding site from autoinhibition. Thus, this regulation could result in local activation of the additional actin-binding site of espin 1 by myosin III in stereocilia.

Original languageEnglish (US)
Pages (from-to)1306-1317
Number of pages12
JournalJournal of cell science
Issue number6
StatePublished - Mar 1 2014



  • Actin
  • Ankyrin repeat
  • Autoinhibition
  • Bundle
  • Espin
  • Hair cell
  • Myosin III
  • Stereocilia

ASJC Scopus subject areas

  • Cell Biology

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