Over one third of all proteins contain metal ions and understanding how these ions provide structural stability, affect folding, and catalyze reactions is critical to understanding metalloprotein structure and function. Many essential biological processes, such as respiration and hydrolytic chemistry, depend on metalloenzymes. A clear understanding of function is essential for solving problems that arise when the proteins misfunction, causing disease. One metalloenzyme, carbonic anhydrase, uses a Zn(II) ion bound by three histidine residues to hydrate CO2, a process that is critical to human health. The goals of this project are 1) to design a simple peptidic construct containing a three histidine metal binding site, 2) to characterize the metal-bound protein, 3) to measure the reactivity of the metalloprotein toward CO2 hydrolysis, and 4) to improve the reactivity by introducing hydrogen binding sites near the active center. To achieve these goals, de novo design principles will be utilized. A single-stranded anti-parallel three-helix protein containing three histidine residues near the C-terminal end will be expressed in E. coli, purified, and bound to Zn(II), Co(II), and Cd(II). Characterization by NMR, EPR, EXAFS, UV/vis, and CD spectroscopies and XRD will give a thorough description of the binding site environment, which is expected to be structurally similar to that of carbonic anhydrase. Using the Zn(II)-bound construct, the activity toward p-nitrophenyl acetate hydrolysis and CO2 hydration will be measured with the expectation of catalytic activity. Finally, hydrogen bonding residues will be incorporated near the active site which should activate the hydroxide ligand on Zn(II) as Thr199 does in carbonic anhydrase. This study will provide a general method for the incorporation of a reactive metal site into a simplified protein construct, result in a carbonic anydrase mimic, and establish the effects of secondary interactions on protein-bound metals. This will further the field of bioinorganic chemistry by moving it one step closer to its ultimate goal of complete control over protein structure and function.
The regulation of CO2 in the blood, a process that is critical for human health, is carried out by the zinc-containing protein carbonic anhydrase. To gain a better understanding of how protein-bound metals catalyze reactions and stabilize structure, a simple protein that will bind zinc and mimic carbonic anhydrase's activity will be designed, synthesized, and studied. The effects to reactivity of changes to the protein structure near the zinc binding site will be studied, giving insight into the importance of substrate interactions.
| Yu, Fangting; Cangelosi, Virginia M; Zastrow, Melissa L et al. (2014) Protein design: toward functional metalloenzymes. Chem Rev 114:3495-578 |
