We report extended pH- and temperature-induced preparation procedures and explore the materials and molecular properties of different types of hydrogels made from human and bovine serum albumin, the major transport protein in the blood of mammals. We describe the diverse range of properties of these hydrogels at three levels: (1) their viscoelastic (macroscopic) behavior, (2) protein secondary structure changes during the gelation process (via ATR-FTIR spectroscopy), and (3) the hydrogel fatty acid (FA) binding capacity and derive from this the generalized tertiary structure through CW EPR spectroscopy. We describe the possibility of preparing hydrogels from serum albumin under mild conditions such as low temperatures (notably below albumin's denaturation temperature) and neutral pH value. As such, the proteins retain most of their native secondary structure. We find that all the combined data indicate a two-stage gelation process that is studied in detail. We summarize these findings and the explored dependences of the gels on pH, temperature, concentration, and incubation time by proposing phase diagrams for both HSA and BSA gel-states. As such, it has become possible to prepare gels that have the desired nanoscopic and macroscopic properties, which can, in future, be tested for, e.g., drug delivery applications.

Significance: The EHD2 protein controls the association of membrane pits termed caveolae to cell surfaces. Caveolae are implicated in muscle, pulmonary, and lipid disorders. We establish functionally, and structurally, how EHD2 cycles between an active, membrane-bound state and an inactive state in solution. We present an approach to resolve the structure of proteins in their membrane-bound state, which is difficult to obtain otherwise. A dramatic conformational change of EHD2 upon membrane binding is demonstrated. ATP binding is required for partial membrane insertion and subsequent oligomerization. In solution, internal regulatory regions inhibit the conformational change. This stringently regulated mechanistic cycle might be prototypical for a large family of proteins involved in membrane fission and may open avenues to control the process in vivo.