title: How a single residue in individual β-thymosin/WH2 domains controls their functions in actin assembly.
abstract: β-Thymosin (βT) and WH2 domains are widespread, intrinsically disordered actin-binding peptides that display significant sequence variability and different regulations of actin self-assembly in motile and morphogenetic processes. Here, we reveal the structural mechanisms by which, in their 1:1 stoichiometric complexes with actin, they either inhibit assembly by sequestering actin monomers like Thymosin-β4, or enhance motility by directing polarized filament assembly like Ciboulot βT. We combined mutational, functional or structural analysis by X-ray crystallography, SAXS (small angle X-ray scattering) and NMR on Thymosin-β4, Ciboulot, TetraThymosinβ and the long WH2 domain of WASP-interacting protein. The latter sequesters G-actin with the same molecular mechanisms as Thymosin-β4. Functionally different βT/WH2 domains differ by distinct dynamics of their C-terminal half interactions with G-actin pointed face. These C-terminal interaction dynamics are controlled by the strength of electrostatic interactions with G-actin. At physiological ionic strength, a single salt bridge with actin located next to their central LKKT/V motif induces G-actin sequestration in both isolated long βT and WH2 domains. The results open perspectives for elucidating the functions of βT/WH2 domains in other modular proteins.
authors.affiliation: Laboratoire d'Enzymologie et Biochimie Structurales, Centre de Recherche de Gif, CNRS, Gif-sur-Yvette, France.
authors.forename: Dominique
authors.initials: D
authors.lastname: Didry
authors.forename: Francois-Xavier
authors.initials: FX
authors.lastname: Cantrelle
authors.forename: Clotilde
authors.initials: C
authors.lastname: Husson
authors.forename: Pierre
authors.initials: P
authors.lastname: Roblin
authors.forename: Anna M Eswara
authors.initials: AM
authors.lastname: Moorthy
authors.forename: Javier
authors.initials: J
authors.lastname: Perez
authors.forename: Christophe
authors.initials: C
authors.lastname: Le Clainche
authors.forename: Maud
authors.initials: M
authors.lastname: Hertzog
authors.forename: Eric
authors.initials: E
authors.lastname: Guittet
authors.forename: Marie-France
authors.initials: MF
authors.lastname: Carlier
authors.forename: Carine
authors.initials: C
authors.lastname: van Heijenoort
authors.forename: Louis
authors.initials: L
authors.lastname: Renault
mesh_terms: D000199:Actins / Q000378:metabolism*; D000595:Amino Acid Sequence; D018360:Crystallography, X-Ray; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D009994:Osmolar Concentration; D053838:Scattering, Small Angle; D017386:Sequence Homology, Amino Acid; D013947:Thymosin / Q000737:chemistry / Q000378:metabolism*
chemical_list: D000199:Actins; D013947:Thymosin