Title

Rational design of synthetic metalloproteins

Date of Award

2013

Document Type

Dissertation

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Photochemical Sciences

First Advisor

Michael Y. Ogawa

Second Advisor

R. Marshall Wilson (Committee Member)

Third Advisor

H. Peter Lu (Committee Member)

Fourth Advisor

R. Michael L. McKay (Committee Member)

Abstract

This dissertation work focuses on the design of metal-binding a-helical coiled coils. They provide a simple yet unique model to study both metal-protein and protein-protein interactions and serve as means to gain knowledge that is required for preparation of synthetic materials with biotechnological and pharmaceutical applications. Originals efforts were devoted to elucidate factors that are important for preparation of the multi-metal centers within a-helical coiled coils. The chapter 3 explored the effect of systematically repacked hydrophobic core on both structural properties and metal-binding abilities of the resulting coiled coils. A series of coiled coils was designed to contain a similar Cys-X-X-Cys metal-binding site but different combinations of isoleucine/leucine residues at the hydrophobic core positions. This yielded triple-stranded coiled-coil assemblies with tightly packed cores, which displayed resistance to thermal and chemical denaturation, and weakly packed three-stranded coiled coils, extremely unstable in the presence of denaturants. The cadmium metal-binding studies showed that all coiled coils analogous were able to host similar polynuclear cadmium-thiolate clusters, but the metal binding occurred cooperatively in the tight variants and through formation of the stable intermediates in the weak variants. The chapter 4 probed the role of the exterior surface residues as first shell ligands. The mutation studies showed that the coiled coil structure can redirect the glutamic residues from the exterior surface towards the hydrophobic core and utilize them to produce the large multi-metal centers. Equipped with insights from the metal-binding studies, the last chapter explored the use of coiled coils for the size-controlled preparation of fluorescent few-atom silver nanoclusters. Incorporation of the Cys-X-X-Cys metal-binding site into three-, four-, and six-stranded a-helical coiled coils produced a family of metallopeptides capable in binding of a different number of silver ions. The chemical reduction of the metal clusters resulted in the appearance of the strong visible fluorescence. Importantly, the emission energies correlated with the size of the encapsulated nanoclusters and showed an excellent consistency with the values predicted by theory. Combined with the narrow emission profiles and excellent chemical stabilities, these clusters serve as attractive candidates for the use as multicolor biological probes.