Folding Factors and Partners for the Intrinsically Disordered Protein Micro-Exon Gene 14 (MEG-14)

The micro-exon genes (MEG) of Schistosoma mansoni, a parasite responsible for the second most widely spread tropical disease, code for small secreted proteins with sequences unique to the Schistosoma_genera. Bioinformatics analyses suggest the soluble domain of the MEG-14 protein will be largely disordered, and using synchrotron radiation circular dichroism spectroscopy, its secondary structure was shown to be essentially completely unfolded in aqueous solution. It does, however, show a strong propensity to fold into more ordered structures under a wide range of conditions. Partial folding was produced by increasing temperature (in a reversible process), contrary to the behavior of most soluble proteins. Furthermore, significant folding was observed in the presence of negatively charged lipids and detergents, but not in zwitterionic or neutral lipids or detergents. Absorption onto a surface followed by dehydration stimulated it to fold into a helical structure, as it did when the aqueous solution was replaced by nonaqueous solvents. Hydration of the dehydrated folded protein was accompanied by complete unfolding. These results support the identification of MEG-14 as a classic intrinsically disordered protein, and open the possibility of its interaction/folding with different partners and factors being related to multifunctional roles and states within the host.