Abstract：
:Fibronectin (FN) is an extracellular matrix (ECM) protein found soluble in corporal fluids or as an insoluble fibrillar component incorporated in the ECM. This phenomenon implicates structural changes that expose FN binding sites and activate the protein to promote intermolecular interactions with other FN. We have investigated, using fluorescence and circular dichroism spectroscopy, the unfolding process of human fibronectin induced by urea in different ionic strength conditions. At any ionic strength, the equilibrium unfolding data are well described by a four-state equilibrium model N <= => I(1) <= =>I(2) <= => U. Fitting this model to experimental values, we have determined the free energy change for the different steps. We found that the N <= => I(1) transition corresponds to a free energy of 10.5 +/- 0.4 kcal/mol. Comparable values of free energy change are generally associated with a partial unfolding of the type III domain. For the I(1) <= => I(2) transition, the free energy change is 7.6 +/- 0.4 kcal/mol at low ionic strength but is twice as low at high ionic strength. This result is consistent with observations indicating that the complete unfolding of the type III domain from partially unfolded forms necessitates about 5 kcal/mol. The third step, I(2) <= => U, which leads to the complete unfolding of fibronectin, corresponds to a free energy change of 14.4 +/- 0.9 kcal/mol at low ionic strength whereas this energy is again twice as low under high ionic strength conditions. This hierarchical unfolding of fibronectin, as well as the stability of the different intermediates controlled by ionic strength demonstrated here, could be important for the understanding of activation of the matrix assembly.
journal_name
Biochemistryjournal_title
Biochemistryauthors
Patel S,Chaffotte AF,Goubard F,Pauthe Edoi
10.1021/bi0347104subject
Has Abstractpub_date
2004-02-17 00:00:00pages
1724-35issue
6eissn
0006-2960issn
1520-4995journal_volume
43pub_type
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