|Abstract: ||The impending energy crisis is one of the biggest challenges that scientists of today face. At the root of this problem lie the dual issues of limited fossil fuel supplies and rising CO2 levels, both of which threaten severe ecological damage. On a more pragmatic note, however, our entire society has been built around facile access to liquid fuels. Thus, any solution to this predicament requires an end product that can be easily assimilated into the current infrastructure.
In contrast to anthropogenic methods, nature has evolved diverse systems to carry out energy conversion reactions. Many, including metalloenzymes such as hydrogenase, carbon monoxide dehydrogenase, and acetyl coenzyme A synthase, can reversibly generate and oxidize small-molecule fuels. However, while these protein systems are highly functional within their native environment, most are costly to isolate, sensitive to external conditions, and generally poorly suited for large-scale application. Additionally, the multimetallic active sites and auxiliary cofactors obscure distinguishing spectroscopic features and render detailed analyses challenging. As a result, the molecular mechanisms of catalysis remain relatively poorly understood, thwarting efforts to build biomimetic synthetic systems that act with the efficacy of native enzymes.
We have approached this problem from a metalloprotein engineering perspective. Azurin and rubredoxin are two of the most well studied proteins within the bioinorganic community. Both are robust platforms, known for their unique spectroscopic features and representative coordination geometries for entire classes of copper- and iron-based proteins; however, neither protein is considered an enzyme. By introducing non-native metals and redesigning the primary and secondary coordination spheres, we have been able to install novel activity into these simple electron transfer proteins. Recent results will be presented demonstrating catalytic hydrogen production, carbon dioxide fixation, and small-molecule activation in these repurposed bioinorganic scaffolds. Optical, vibrational, and magnetic resonance spectroscopic techniques have been used in conjunction with density functional theory calculations to probe the active-site structures across different states, with the intent of characterizing the catalytic mechanisms. These findings will be discussed in the context of identifying the fundamental principles underlying highly active native enzymes and applying those principles towards engineering effective model metalloproteins for energy conversion reactions.|