The heparin III-binding domain of fibronectin (III4-5 repeats) binds to fibronectin and inhibits fibronectin matrix assembly.
Fibronectin matrix assembly involves interactions among various regions of the molecule, which contribute to elongation and stabilization of the fibrils. In this study, we examined the possible role of the heparin III domain of fibronectin (repeats III4-5) in fibronectin fibrillogenesis. We show that a recombinant fragment comprising these repeats (FNIII4-5 fragment) blocked fibronectin fibril formation and the incorporation of 125I-fibronectin into cell layers. Binding assays using a biosensor revealed that FNIII4-5 bound fibronectin and the amino-terminal 70 kDa and 29 kDa fragments. It also bound to itself, indicating a previously unidentified self-association site in repeats III4-5. These interactions were specific since FNIII4-5 did not bind to the FNIII7-10 fragment, representing a central region in fibronectin. The fibronectin-binding property of the III4-5 domain, but not its matrix assembly inhibitory function, was apparently cryptic in larger fragments. By mutating the arginine residues in the WTPPRAQITGYRLTVGLTRR proteoglycan-binding sequence (HBP/III5 site) of FNIII4-5 [Moyano, J.V., Carnemolla, B., Albar, J.P., Leprini, A., Gaggero, B., Zardi, L., Garcia-Pardo, A., 1999. Cooperative role for activated alpha4beta1 integrin and chondroitin sulfate proteoglycans in cell adhesion to the heparin III domain of fibronectin. Identification of a novel heparin and cell binding sequence in repeat III5. J. Biol. Chem. 274, 135-142.], we found that the first two arginine residues in HBP/III5 were involved in the fibronectin-binding property of FNIII4-5, while the last two arginine residues in HBP/III5 were required for inhibition of matrix assembly and the binding of 125I-fibronectin to cell layers. Both properties appear to function independently from each other, depending on the conformation of the fibronectin dimer.
Maqueda
Alfredo
A
Departamento de Fisiopatología Celular y Molecular, Centro de Investigaciones Biológicas, CSIC, Ramiro de Maeztu 9, 28040 Madrid, Spain.
Moyano
José V
JV
Hernández Del Cerro
Mercedes
M
Peters
Donna M
DM
Garcia-Pardo
Angeles
A
D000595:Amino Acid Sequence; D001665:Binding Sites; D005109:Extracellular Matrix / Q000378:metabolism*; D005353:Fibronectins / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D006493:Heparin / Q000378:metabolism*; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D010446:Peptide Fragments / Q000737:chemistry* / Q000378:metabolism*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D012995:Solubility
D005353:Fibronectins; D010446:Peptide Fragments; D006493:Heparin