title: Identification and characterization of multiple similar ligand-binding repeats in filamin: implication on filamin-mediated receptor clustering and cross-talk.
abstract: The actin-binding protein filamin links membrane receptors to the underlying cytoskeleton. The cytoplasmic domains of these membrane receptors have been shown to bind to various filamin immunoglobulin repeats. Notably, among 24 human filamin repeats, repeat 17 was reported to specifically bind to platelet receptor glycoprotein Ibalpha and repeat 21 to integrins. However, a complete sequence alignment of all 24 human filamin repeats reveals that repeats 17 and 21 actually belong to a distinct filamin repeat subgroup (containing repeats 4, 9, 12, 17, 19, 21, and 23) that shares a conserved ligand-binding site. Using isothermal calorimetry and NMR analyses, we show that all repeats in this subgroup can actually bind glycoprotein Ibalpha, integrins, and a cytoskeleton regulator migfilin in similar manners. These data provide a new view on the ligand specificity of the filamin repeats. They also suggest a multiple ligand binding mechanism where similar repeats within a filamin monomer may promote receptor clustering or receptor cross-talking for regulation of the cytoskeleton organization and diverse filamin-mediated cellular activities.
authors.affiliation: Department of Molecular Cardiology, Lerner Research Institute, Cleveland Clinic, Cleveland, Ohio 44195 , USA.
authors.forename: Sujay Subbayya
authors.initials: SS
authors.lastname: Ithychanda
authors.forename: Dennis
authors.initials: D
authors.lastname: Hsu
authors.forename: Hanhan
authors.initials: H
authors.lastname: Li
authors.forename: Linda
authors.initials: L
authors.lastname: Yan
authors.forename: David D
authors.initials: DD
authors.lastname: Liu
authors.forename: Darwen
authors.initials: D
authors.lastname: Liu
authors.forename: Mitali
authors.initials: M
authors.lastname: Das
authors.forename: Edward F
authors.initials: EF
authors.lastname: Plow
authors.forename: Jun
authors.initials: J
authors.lastname: Qin
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002151:Calorimetry; D015815:Cell Adhesion Molecules / Q000235:genetics / Q000378:metabolism; D003285:Contractile Proteins / Q000737:chemistry / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D003598:Cytoskeletal Proteins / Q000235:genetics / Q000378:metabolism; D064448:Filamins; D006801:Humans; D016023:Integrins / Q000235:genetics / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000378:metabolism; D008840:Microfilament Proteins / Q000737:chemistry / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D010802:Phylogeny; D019038:Platelet Glycoprotein GPIb-IX Complex; D020033:Protein Isoforms / Q000737:chemistry / Q000145:classification / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D015398:Signal Transduction / Q000502:physiology*
chemical_list: D015815:Cell Adhesion Molecules; D003285:Contractile Proteins; D003598:Cytoskeletal Proteins; C473794:FBLIM1 protein, human; D064448:Filamins; D016023:Integrins; D008562:Membrane Glycoproteins; D008840:Microfilament Proteins; D019038:Platelet Glycoprotein GPIb-IX Complex; D020033:Protein Isoforms; C094990:adhesion receptor