Hydrogels from serum albumin in a molten globule-like state.

We demonstrate that a molten globule-like (MG) state of a protein, usually described as a compact yet non-folded conformation that is only present in a narrow and delicate parameter range, is preserved in the high concentration environment of the protein hydrogel. We reveal mainly by means of electron paramagnetic resonance (EPR) spectroscopy that bovine serum albumin (BSA) retains the known basic MG state after a hydrogel has been formed from 20 wt% precursor solutions. At pH values of ~11.4, BSA hydrogels made from MG-BSA remain stable for weeks, while gels formed at slightly different (~0.2) pH units above and below the MG-state value dissolve into viscous solutions. On the contrary, when hydrophobic screening agents are added such as amphiphilic, EPR-active stearic acid derivatives (16-DOXYL-stearic acid, 16-DSA), the MG-state based hydrogel is the least long-lived, as the hydrophobic interaction of delicately exposed hydrophobic patches of BSA molecules is screened by the amphiphilic molecules. These bio- and polymer-physically unexpected findings may lead to new bio-compatible MG-based hydrogels that display novel properties in comparison to conventional gels.