Computational Design of a Self-Assembling Metalloprotein

Genetically encoded non-canonical amino acids (NCAAs) have allowed researchers to access functionalities that would be otherwise unavailable with the naturally-occurring amino acids. The metal-chelating NCAA (2,2'-bipyridin-5yl)alanine (Bpy-ala) has recently been employed, in tandem with computational modeling, to drive the assembly of a homotrimeric protein complex in the presence of a metal ion, specifically Fe(II). While a successful design was identified to form a homotrimeric complex with an iron-trisbipyridyl [Fe(Bpy-ala)3]2+ core when expressed in E. coli, its subsequent utility was marred by an excessively strong protein-protein interaction thus leading to a lack of metal-dependency. This thesis describes principles of protein design and characterization used to reduce the favorability of the apo protein complex in solution, resulting in the experimental verification of a mutant that undergoes facile, reversible complex assembly and disassembly in the presence or absence of Fe(II), respectively. The addition of other metal ions, such as Co(II) or Ni(II), yields products that show some level of assembly, although not with the same efficiency as Fe(II) addition, necessitating a better description of the energetics and kinetics of the system. Current studies are ongoing to examine the redox properties of the complex, as well as the kinetics of the metal-mediated self-assembly. Attempts to nucleate the trimer with Ru(II), forming a [Ru(Bpy)3]2+ complex with its interesting photophysical, photochemical, and photoredox properties, have not been met with substantial success, as coordination of the low-spin d6 metal ion often requires harsh conditions. However, due to the unique stability of the TRI_05 complexes, many approaches are available to this end, and experiments are underway to elucidate the proper conditions.