Statistical conformation of human plasma fibronectin

Fibronectin is a multifunctional glycoprotein (molecular mass, M = 530 kg/m ol) of the extra cellular matrix (ECM) having a major role in cell adhesion . In physiological conditions, the conformation of this protein still remai ns debated and controversial. Here, we present a set of results obtained by scattering experiments. In "native" conditions, the radius of gyration (R- g = 15.3 +/- 0.3 nm) was determined by static light scattering as well. as small-angle neutron scattering. The hydrodynamic radius (R-H = 11.5 +/- 0.1 nm) was deduced from quasi-elastic light scattering measurements. These re sults imply a low internal concentration (M/R-g/H(3)) compared to that of u sual globular proteins. This is also confirmed by the ratio R-H/R-g = 0.75 +/- 0.02 consistent with a Gaussian chain, whereas R-H/R-g = 1.3 for spheri cal shaped molecules. However, adding a denaturing agent (urea 8 M) increas es R-g by a factor 3. This means that fibronectin "native" chain is not eit her completely unfolded. The average shape of fibronectin conformation was also probed by small-angle neutron scattering performed for reverse scatter ing vector q(-1) smaller than R-g (0.2 < q(-1) < 15 nm). The measured form factor is in complete agreement with the form factor of a random string of 56 beads of 5 nm diameter. It rules out the possibility of unfolded chain a s well as globular structures. These results have structural and biological implications as far as ECM organization is concerned.