title: The tryptophan-rich motifs of the thrombospondin type 1 repeats bind VLAL motifs in the latent transforming growth factor-beta complex.
abstract: Transforming growth factor-beta (TGF-beta) is secreted as a latent complex of the latency-associated peptide (LAP) and the mature domain, which must be activated for TGF-beta to signal. We previously identified thrombospondin 1 (TSP1) as a physiologic activator of TGF-beta in vitro and in vivo. The WSXW sequences in the type 1 repeats of TSP1 interact with the mature domain of TGF-beta, and WSXW peptides inhibit TSP1-mediated activation by blocking TSP1 binding to the TGF-beta latent complex. However, the binding site for the WSXW sequence was not identified. In this report, we show that the WSXW sequences bind the (61)VLAL sequence in mature TGF-beta and also bind (77)VLAL in LAP. A glutathione S-transferase (GST) fusion protein of the second TSP1 type 1 repeat (GST-TSR2) binds immobilized VLAL peptide. VLAL peptides inhibit binding of LAP and mature TGF-beta to soluble GST-TSR2 and immobilized WSXW peptide. VLAL peptide inhibits TSP1-mediated activation of recombinant and endothelial cell-derived latent TGF-beta. Furthermore, TGF-beta or LAP deleted in the VLAL sequence fails to bind immobilized WSXW or soluble GST-TSR2, indicating that binding to both VLAL sequences is important for association of TSP1 and the latent complex. Additionally, TSP1 is unable to activate latent TGF-beta when VLAL is deleted from the mature domain. These data show that the WSXW motif binds VLAL on both LAP and mature TGF-beta, and these interactions are critical for TSP1-mediated activation of the TGF-beta latent complex.
authors.affiliation: Medical Scientist Training Program, the Cell Adhesion and Matrix Research Center, University of Alabama, Birmingham, Alabama 35294-0019, USA.
authors.forename: Geoffrey D
authors.initials: GD
authors.lastname: Young
authors.forename: Joanne E
authors.initials: JE
authors.lastname: Murphy-Ullrich
mesh_terms: D020816:Amino Acid Motifs; D000818:Animals; D001665:Binding Sites; D002460:Cell Line; D006801:Humans; D046911:Macromolecular Substances; D051379:Mice; D018345:Mice, Knockout; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010455:Peptides / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D019700:Thrombospondin 1 / Q000235:genetics* / Q000378:metabolism*; D016212:Transforming Growth Factor beta / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D014364:Tryptophan / Q000378:metabolism*
chemical_list: D046911:Macromolecular Substances; D010455:Peptides; D011993:Recombinant Fusion Proteins; D019700:Thrombospondin 1; D016212:Transforming Growth Factor beta; D014364:Tryptophan