Interactions of tensin with actin and identification of its three distinct actin-binding domains.
Tensin, a 200-kD phosphoprotein of focal contacts, contains sequence homologies to Src (SH2 domain), and several actin-binding proteins. These features suggest that tensin may link the cell membrane to the cytoskeleton and respond directly to tyrosine kinase signalling pathways. Here we identify three distinct actin-binding domains within tensin. Recombinant tensin purified after overexpression by a baculovirus system binds to actin filaments with Kd = 0.1 microM, cross-links actin filaments at a molar ratio of 1:10 (tensin/actin), and retards actin assembly by barbed end capping with Kd = 20 nM. Tensin fragments were constructed and expressed as fusion proteins to map domains having these activities. Three regions from tensin interact with actin: two regions composed of amino acids 1 to 263 and 263 to 463, cosediment with F-actin but do not alter the kinetics of actin assembly; a region composed of amino acids 888-989, with sequence homology to insertin, retards actin polymerization. A claw-shaped tensin dimer would have six potential actin-binding sites and could embrace the ends of two actin filaments at focal contacts.
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Dana-Farber Cancer Institute, Boston, Massachusetts 02115.
Janmey
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Hartwig
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Chen
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LB
D008841:Actin Cytoskeleton / Q000648:ultrastructure; D000199:Actins / Q000378:metabolism* / Q000648:ultrastructure; D000818:Animals; D001665:Binding Sites; D002645:Chickens; D008840:Microfilament Proteins / Q000378:metabolism*; D009119:Muscle Contraction; D011485:Protein Binding; D011993:Recombinant Fusion Proteins; D000070876:Tensins
D000199:Actins; D008840:Microfilament Proteins; D011993:Recombinant Fusion Proteins; D000070876:Tensins