title: The compact conformation of fibronectin is determined by intramolecular ionic interactions.
abstract: Fibronectin exists in a compact or extended conformation, depending upon environmental pH and salt concentration. Using recombinant fragments expressed in bacteria and baculovirus, we determined the domains responsible for producing fibronectin's compact conformation. Our velocity and equilibrium sedimentation data show that FN2-14 (a protein containing FN-III domains 2 through 14) forms dimers in low salt. Experiments with smaller fragments indicates that the compact conformation is produced by binding of FN12-14 of one subunit to FN2-3 of the other subunit in the dimer. The binding is weakened at higher salt concentrations, implying an electrostatic interaction. Furthermore, segment FN7-14+A, which contains the alternatively spliced A domain between FN11 and 12, forms dimers, whereas FN7-14 without A does not. Segment FN12-14+A also forms dimers, but the isolated A domain does not. These data imply an association of domain A with FN12-14, and the presence of A may favor an open conformation by competing with FN2-3 for binding to FN12-14.
authors.affiliation: Department of Cell Biology, Duke University Medical Center, Durham, North Carolina 27710, USA.
authors.forename: K J
authors.initials: KJ
authors.lastname: Johnson
authors.forename: H
authors.initials: H
authors.lastname: Sage
authors.forename: G
authors.initials: G
authors.lastname: Briscoe
authors.forename: H P
authors.initials: HP
authors.lastname: Erickson
mesh_terms: D000818:Animals; D002417:Cattle; D019281:Dimerization; D005353:Fibronectins / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D016023:Integrins / Q000737:chemistry; D008958:Models, Molecular; D010446:Peptide Fragments / Q000737:chemistry; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics; D012492:Salts / Q000494:pharmacology; D055672:Static Electricity; D013820:Thermolysin
chemical_list: D005353:Fibronectins; D016023:Integrins; D010446:Peptide Fragments; D011994:Recombinant Proteins; D012492:Salts; D013820:Thermolysin