Specific sequence motif of 8-Cys repeats of TGF-beta binding proteins, LTBPs, creates a hydrophobic interaction surface for binding of small latent TGF-beta.
Transforming growth factor (TGF)-betas are secreted in large latent complexes consisting of TGF-beta, its N-terminal latency-associated peptide (LAP) propeptide, and latent TGF-beta binding protein (LTBP). LTBPs are required for secretion and subsequent deposition of TGF-beta into the extracellular matrix. TGF-beta1 associates with the 3(rd) 8-Cys repeat of LTBP-1 by LAP. All LTBPs, as well as fibrillins, contain multiple 8-Cys repeats. We analyzed the abilities of fibrillins and LTBPs to bind latent TGF-beta by their 8-Cys repeats. 8-Cys repeat was found to interact with TGF-beta1*LAP by direct cysteine bridging. LTBP-1 and LTBP-3 bound efficiently all TGF-beta isoforms, LTBP-4 had a much weaker binding capacity, whereas LTBP-2 as well as fibrillins -1 and -2 were negative. A short, specific TGF-beta binding motif was identified in the TGF-beta binding 8-Cys repeats. Deletion of this motif in the 3(rd) 8-Cys repeat of LTBP-1 resulted in loss of TGF-beta*LAP binding ability, while its inclusion in non-TGF-beta binding 3(rd) 8-Cys repeat of LTBP-2 resulted in TGF-beta binding. Molecular modeling of the 8-Cys repeats revealed a hydrophobic interaction surface and lack of three stabilizing hydrogen bonds introduced by the TGF-beta binding motif necessary for the formation of the TGF-beta*LAP - 8-Cys repeat complex inside the cells.
Departments of Virology and Pathology, The Haartman Institute, University of Helsinki, Finland.
J
J
Saharinen
J
J
Keski-Oja
D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D002352:Carrier Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D003545:Cysteine / Q000737:chemistry*; D004847:Epithelial Cells; D000071837:Fibrillins; D005347:Fibroblasts; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D053779:Latent TGF-beta Binding Proteins; D008840:Microfilament Proteins / Q000737:chemistry / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011485:Protein Binding; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D016415:Sequence Alignment; D014162:Transfection; D016212:Transforming Growth Factor beta / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
D002352:Carrier Proteins; D000071837:Fibrillins; D047908:Intracellular Signaling Peptides and Proteins; C509032:LTBP1 protein, human; C509035:LTBP2 protein, human; C509038:LTBP3 protein, human; C509040:LTBP4 protein, human; D053779:Latent TGF-beta Binding Proteins; D008840:Microfilament Proteins; D020033:Protein Isoforms; D011993:Recombinant Fusion Proteins; D016212:Transforming Growth Factor beta; D003545:Cysteine