Investigating ferritin-metallo interactions

Here, we describe two different studies using ferritin protein as a model cage protein that interacts with metals. In the first project, we investigated the ability for thermophilic ferritin (of the archaeon Archaeglobus fulgidus) to interface in a native-like fashion with 5- nm gold nanoparticles (AuNPs). Thermophilic ferritin (tF) can uniquely disassemble from a 24mer spherical cage- structure into 2mer subunits by being immersed in a solution of low ionic strength. We took advantage of this property by interfacing tF protein in 2mer form with 5-nm AuNPs. A novel self-assembling system resulted whereby the 2mer subunits assembled around the AuNP. We confirmed that the new tF-AuNP system retained the native ferritin properties of alpha-helical secondary structure, thermal stability, and enzymatic ferroxidation ability. This unique ferritin-NP system has potential applications as a functionalizable sensing or imaging bio-compatible agent. In our second project, we studied the possible reactivity between two different ferritin proteins (horse spleen apoferritin and human H-chain apoferritin) and two commonly used Gd-based MRI-contrast agents: Omniscan (Gd-DTPA-BMA) and Magnevist (Gd-DTPA(2-)). This project began primarily in response to the realization that administration of certain Gd-chelated contrast agents to patients with weak kidney functions caused the patients to develop the disease, nephrogenic systemic fibrosis (NSF). The increased circulation time (2 h to \u3e 24 h) of the contrast agents in said patients is the primary reason for the development of the disease, meaning that the stability of the Gd chelated agents, in vivo, is on the order of 24 h or less. Investigation by other groups have further found that the administered Gd complexes affect the iron metabolism of all patients. Since ferritin controls iron metabolism processes, we hypothesized that the Gd complexes interact with ferritin, causing changes in iron levels, and perhaps, the development of NSF. Through NMR-D and relaxivity measurements, we conclusively discovered that Gd contrast agents and Gd(III) ions do interact with ferritin proteins; but our findings are not proof that Gd-ferritin interactions cause the disorder -- further experiments will be needed to elucidate the mechanism by which NSF develops