Structure of the Intrinsically Disordered Protein Otholith in Solution at Different Protein and Salt Concentrations

Two members of the intrinsically disordered proteins (IDP) family (OMM-64 and STM) have been studied by means of small angle neutron scattering (SANS), dynamic light scattering (DLS) and fluorescence correlation spectroscopy (FCS). SANS curves of the proteins in D2O buffers have been measured for a range of Na+ and Ca2+ salts concentrations. The same samples have been measured using DLS in order to estimate their apparent hydrodynamic radii (Rh) and the scattering intensity in the q = 0 limit. The size of the proteins as a function of Na+ and Ca2+ concentrations had been measured in nano-molar concentrations using FCS. Fits to the SANS data suggest a coiled structure of the proteins in solution. For the first time SANS curves of proteins embedded in calcium carbonate crystals have been measured. Also a coiled structure has been found (slope = -2). Exact values of the radius of gyration (Rg) from SANS need measurements at smaller q-values