Biochemistry Seminar: Brian Gibney
Wed, Mar 05
12:00 PM — 1:00 PM
MarshakCity College of New York160 Convent Ave
Brian Gibney, Brooklyn College, "Zinc Protein Folding: Lessons from Synthetic Peptides"Brian Gibney, Assoc. Prof. of Chemistry, Brooklyn College, will give a talk on "Zinc Protein Folding: Lessons from Synthetic Peptides."
ABSTRACT: Nature utilizes a variety of cofactors and prosthetic groups to augment protein structure and function. Zn(II) is one of the most pervasive metal cofactors in biology, serving proteins in both catalytic and structural capacities. Zinc finger transcription factors represent the largest single class of metalloproteins in the human genome. Binding of Zn(II) to their canonical Cys4, Cys3His1 or Cys2His2 sites results in metal-induced protein folding events required to achieve their proper structure for biological activity. The thermodynamic contribution of Zn(II) in each of these coordination spheres toward protein folding is poorly understood because of the coupled nature of the metal-ligand and protein-protein interactions. Our approach to the study of metalloproteins is to engineer and fabricate peptide structures that incorporate metal cofactors toward the goal of generating molecular maquettes, protein-based synthetic analogues. Herein, we employ a 16 amino acid peptide, which is unstructured in the apo- and Zn(II)-bound states, to determine the maximal thermodynamic affinity of Zn(II) for the Cys4, Cys3His1 and Cys2His2 ligand sets with minimal interference from protein folding effects. Using a combination of potentiometry, isothermal titration fluorimetry and isothermal titration calorimetry (ITC), the conditional dissociation constants, Kd values, for each ligand set have been determined over the pH range of 5.0 to 9.0. These data allow for the determination of the pH independent formation constants, KfML, for each coordination motif and reveal that Zn(II) binding is entropically driven due to dehydration of the metal and the apo-peptide scaffold. The KfML values reveal that the cysteine thiolate is a better ligand than the histidine imidazole, however proton competition at physiological pH renders Cys and His equivalent. These results are used to reveal the energetic cost of protein folding in natural Zn(II) proteins, heretofore unknown values in systems where protein folding is coupled to metal ion binding.