Author

Hsiau-Wei Lee

Date of Award

8-4-2008

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

First Advisor

Dr. Jenny J Yang - Chair

Second Advisor

Dr. Jeffrey L Urbauer

Third Advisor

Dr. James H Prestegard

Fourth Advisor

Dr. David D Wilson

Abstract

Calmodulin is an essential EF-hand protein with a helix-loop-helix calcium binding motif. Understanding Ca(II) dependent activation of calmodulin and other EF-hand proteins is limited by Ca(II)-induced conformational change, multiple and cooperative binding of Ca(II) ions, and interactions between the paired EF-hand motifs. The goal of this research project is to probe key determinants for calcium binding properties and pairing interactions at the site specific level using a grafting approach and high resolution NMR. An individual Ca(II) binding site of the EF-hand motifs of calmodulin was grafted into a non-calcium dependent protein, CD2, to bypass limitations associated with natural EF-hand proteins and peptide fragments. Using high resolution NMR, we have shown that the grafted EF-loop III of calmodulin in the host protein retains its native conformation with a strong loop and β-conformation preference. Grafted ligand residues in the engineered protein are directly involved in binding of Ca(II) and La(III). The NMR studies support our hypothesis that both ligand arrangement and dynamic properties play essential role in tuning Ca(II) binding affinities. Using pulse-field diffusion NMR and protein engineering, we further demonstrated that grafted EF- loop remains as a monomer. Although the EF-loop with flanking helices dimerizes in the presence of Ca(II). Additionally, removal of conserved hydrophobic residues at the flanking helices of the EF-hand motif leads to be monomer in the absence and presence of metal ions. Our results suggest that conserved hydrophobic residues are essential for the pair-paired interaction in the coupled EF-hand protein. We have shown that our developed grafting approach can be applied to probe intrinsic Ca(II) binding affinities of different Ca(II) binding sites.

Included in

Chemistry Commons

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