Recreating Bioenergetic Elements In Protein Maquettes
In all organisms, protein-mediated electron transfers underlie energy metabolism and countless other critical metabolic pathways. Deciphering the factors governing electron transfers offers enormous practical value, including finding reliable guidelines for metabolic engineering to produce clean solar fuels. Protein maquettes provide simple, flexible scaffolds to study biological electron transfer processes. The maquette approach to protein design builds man-made oxidoreductases from first principles with minimal reference to natural protein sequences. This scheme has produced impressive in vitro and in vivo results to replicate the functions of natural oxidoreductases using simple, straightforward α-helical bundles. The redox function of maquettes has so far been limited to electron transfers within a single water-soluble molecule. This work extends the maquette project to examine electron transfers A) between diffusing redox partners and B) in amphiphilic proteins. Nature employs complimentary electrostatic surfaces to bring diffusing redox proteins together, and a series of maquettes of varying surface charge demonstrate that the same principles apply to flexible manmade proteins. A heme-binding maquette of complimentary surface charge is shown to reduce natural cytochrome c at physiological rates, while a maquette variant similar in charge to cyt c shows a far weaker interaction. The ionic strength dependence of these interactions is shown to be broadly similar to that in natural proteins. This work also presents the first intra-protein redox function in a de novo amphiphilic protein and describes progress toward transmembrane electron transfer analogous to that in the cytochrome bc1 complex. These functional achievements are remarkable given that the proteins are designed from first principles without atomically resolved structures, and they hold promise for future efforts in applying artificial proteins to new metabolic pathways.
Bohdana M. Discher