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Biochemistry Seminar: Brian Gibney

  • Date
    Wed, Mar 05

    Time
    12:00 PM — 1:00 PM

    Address
    Marshak
    City College of New York
    160 Convent Ave

    Location
    Marshak, MR-1027

    p: 212.650.8803

    Admission
    Free

  • Event Details

    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.
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