title: Characterization and regulation of an additional actin-filament-binding site in large isoforms of the stereocilia actin-bundling protein espin.
abstract: 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 actin-filament-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 N-terminal 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.
authors.affiliation: Department of Cell and Molecular Biology, Northwestern University Feinberg School of Medicine, Chicago, IL 60611 USA.
authors.forename: Lili
authors.initials: L
authors.lastname: Zheng
authors.forename: Dina M
authors.initials: DM
authors.lastname: Beeler
authors.forename: James R
authors.initials: JR
authors.lastname: Bartles
mesh_terms: D000199:Actins / Q000737:chemistry / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002923:Cilia / Q000378:metabolism; D006801:Humans; D018374:LLC-PK1 Cells; D051379:Mice; D008840:Microfilament Proteins / Q000737:chemistry* / Q000378:metabolism; D008871:Microvilli / Q000378:metabolism; D008969:Molecular Sequence Data; D054730:Protein Interaction Domains and Motifs; D020033:Protein Isoforms; D055503:Protein Multimerization; D051381:Rats; D013552:Swine
chemical_list: D000199:Actins; C493274:ESPN protein, human; D008840:Microfilament Proteins; D020033:Protein Isoforms
keywords: Actin; Ankyrin repeat; Autoinhibition; Bundle; Espin; Hair cell; Myosin III; Stereocilia