Electron transfer reactions are vital for life: they are the essential steps in all the major biological energy conservation pathways and the rate of electron transfer sometimes determines the fate of energy flow. While the rates of electron transfer over 1-2 nanometers in proteins can largely be described by well-known theories, it is not well understood how these processes scale to microscopic distances, for example, micrometer length microbial nanowires. Electron transfer reactions are known to be highly sensitive to the chemical properties of the electron carriers and distances between carriers, yet, this information is not available for naturally occurring microbial nanowires. On the other hand, microbial nanowires have inspired the development of novel biological conductive materials and bioelectronics, although these biomimicking materials would significantly benefit from a higher degree of structural definition, which would greatly improve rational redesign.This dissertation work presents two distinct approaches for arranging electron carriers (heme) into structurally defined arrays that can facilitate electron transfer:1) A crystalline lattice of small tetraheme cytochromes that form a well-defined, three-dimensional network of closely spaced redox centers was used to demonstrate the multi-step electron hopping over a micrometer scale.2) A heme attachment strategy was developed that allows one to introduce redox active cofactor hemes into non-heme-binding proteins, while maintaining the proteins' original function. Adding hemes to a nanotube-forming self-assembling protein was used to demonstrate the potential of this strategy to form a structurally defined heme array.The first crystal approach provides detailed information about structure and electronic states which can be used as a platform for testing theories, while the second heme-attaching approach is an engineering platform that allows researchers to introduce redox properties into other well-studied proteins with minimal effort. These two approaches, from two perspectives, lay the foundation of building structurally defined architectures for the understanding of microbial nanowires and the application of biological long-range electron transfer materials.
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