Complex Effects of Molecular Chaperones on the Aggregation and Refolding of Fibroblast Growth Factor-1

Abstract

Fibroblast growth factor one (FGF-1) exists in a molten globule (MG)-like state under physiological conditions (neutral pH, 37°C). It has been proposed that this form of the protein may be involved in its atypical membrane transport properties. Macromolecular chaperones have been shown to bind to MG states of proteins as well as to be involved in protein membrane transport. We have therefore examined the effect of such proteins on the aggregation and refolding of FGF-1 to evaluate whether they might play a role in FGF-1 transport. The proposed chaperone α-crystallin was found to strongly inhibit the aggregation of the MG state of FGF-1. Curiously, two other proteins of similar size and charge (thyroglobulin and a monoclonal IgM immunoglobulin) with no previously reported chaperone properties were also found to have a related effect. In contrast, the chaperone GroEL/ES induced further aggregation of MG-like FGF-1 but had no effect on the native conformation. Both chaperones stimulated refolding to the native state (25°C) but had no detectable effect when FGF-1 was refolded to the MG state (37°C). This suggests that disordered intermediates are present in the folding pathways of the native and MG-like FGF conformations which differ from the MG-like state induced under physiological conditions. FGF-1 does, therefore, interact with molecular chaperones, although this may involve both the MG and the native states of the protein.