title: Microtubule-associated protein 4 binds to actin filaments and modulates their properties.
abstract: We previously reported that an isoform of microtubule-associated protein 4 (MAP4) is localized to the distal area of developing neurites, where microtubules are relatively scarce, raising the possibility that MAP4 interacts with another major cytoskeletal component, actin filaments. In the present study, we examined the in vitro interaction between MAP4 and actin filaments, using bacterially expressed MAP4 and its truncated fragments. Sedimentation assays revealed that MAP4 and its microtubule-binding domain fragments bind to actin filaments under physiological conditions. The apparent dissociation constant and the binding stoichiometry of the fragments to actin were about 0.1 µm and 1 : 3 (MAP4/actin), respectively. Molecular dissection studies revealed that the actin-binding site on MAP4 is situated at the C-terminal part of the proline-rich region, where the microtubule-binding site is also located. Electron microscopy revealed that the MAP4-bound actin filaments become straighter and longer and that the number of actin bundles increases with greater concentrations of added MAP4 fragment, indicating that MAP4 binding alters the properties of the actin filaments. A multiple sequence alignment of the proline-rich regions of MAP4 and tau revealed two putative actin-binding consensus sequences.
authors.affiliation: Department of Biological Sciences, Kanagawa University, Tsuchiya 2946, Hiratsuka, Kanagawa 259-1293, Japan. kazuyuki_matsushima@yahoo.co.jp
authors.forename: Kazuyuki
authors.initials: K
authors.lastname: Matsushima
authors.forename: Kiyotaka
authors.initials: K
authors.lastname: Tokuraku
authors.forename: Mohammad Rubayet
authors.initials: MR
authors.lastname: Hasan
authors.forename: Susumu
authors.initials: S
authors.lastname: Kotani
mesh_terms: D008841:Actin Cytoskeleton / Q000378:metabolism* / Q000648:ultrastructure; D000199:Actins / Q000737:chemistry / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002417:Cattle; D004591:Electrophoresis, Polyacrylamide Gel; D015151:Immunoblotting; D007700:Kinetics; D008854:Microscopy, Electron; D008869:Microtubule-Associated Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008870:Microtubules / Q000737:chemistry / Q000378:metabolism; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism; D011392:Proline / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D017386:Sequence Homology, Amino Acid
chemical_list: D000199:Actins; D008869:Microtubule-Associated Proteins; D010446:Peptide Fragments; D011392:Proline