title: Myosin IIIB uses an actin-binding motif in its espin-1 cargo to reach the tips of actin protrusions.
abstract: Myosin IIIA (MYO3A) targets actin protrusion tips using a motility mechanism dependent on both motor and tail actin-binding activity [1]. We show that myosin IIIB (MYO3B) lacks tail actin-binding activity and is unable to target COS7 cell filopodia tips, yet is somehow able to target stereocilia tips. Strikingly, when MYO3B is coexpressed with espin-1 (ESPN1), a MYO3A cargo protein endogenously expressed in stereocilia [2], MYO3B targets and carries ESPN1 to COS7 filopodia tips. We show that this tip localization is lost when we remove the ESPN1 C terminus actin-binding site. We also demonstrate that, like MYO3A [2], MYO3B can elongate filopodia by transporting ESPN1 to the polymerizing end of actin filaments. The mutual dependence of MYO3B and ESPN1 for tip localization reveals a novel mechanism for the cell to regulate myosin tip localization via a reciprocal relationship with cargo that directly participates in actin binding for motility. Our results are consistent with a novel form of motility for class III myosins that requires both motor and tail domain actin-binding activity and show that the actin-binding tail can be replaced by actin-binding cargo. This study also provides a framework to better understand the late-onset hearing loss phenotype in patients with MYO3A mutations.
authors.affiliation: Laboratory of Cell Structure and Dynamics, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: Raymond C
authors.initials: RC
authors.lastname: Merritt
authors.forename: Uri
authors.initials: U
authors.lastname: Manor
authors.forename: Felipe T
authors.initials: FT
authors.lastname: Salles
authors.forename: M'hamed
authors.initials: M
authors.lastname: Grati
authors.forename: Andrea C
authors.initials: AC
authors.lastname: Dose
authors.forename: William C
authors.initials: WC
authors.lastname: Unrath
authors.forename: Omar A
authors.initials: OA
authors.lastname: Quintero
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Yengo
authors.forename: Bechara
authors.initials: B
authors.lastname: Kachar
mesh_terms: D008841:Actin Cytoskeleton / Q000378:metabolism*; D000199:Actins / Q000378:metabolism; D020816:Amino Acid Motifs; D000818:Animals; D019556:COS Cells; D002522:Chlorocebus aethiops; D006801:Humans; D051379:Mice; D008840:Microfilament Proteins / Q000737:chemistry / Q000378:metabolism*; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D018995:Myosin Heavy Chains / Q000378:metabolism*; D025102:Myosin Type III / Q000378:metabolism*; D016133:Polymerase Chain Reaction; D011485:Protein Binding; D021381:Protein Transport; D011554:Pseudopodia / Q000378:metabolism / Q000648:ultrastructure; D051381:Rats; D059547:Stereocilia / Q000378:metabolism; D014162:Transfection
chemical_list: D000199:Actins; C558785:MYO3A protein, mouse; C572903:MYO3B protein, mouse; D008840:Microfilament Proteins; C104108:espin protein, mouse; D025102:Myosin Type III; D018995:Myosin Heavy Chains