Dissertation/Thesis Abstract

Surface-induced peptide folding
by Capriotti, Lisa A., Ph.D., University of Delaware, 2009, 346; 3360285
Abstract (Summary)

This thesis details the novel theory and characterization of surface-induced peptide folding as a mechanism of biological activation with potential in targeted drug delivery and activity. The design of two hydroxyapatite (HA)-folding peptides was based on the bone-binding protein, osteocalcin. The amino-terminal helix of osteocalcin contains three γ-carboxyglutamic acid (Gla) residues on the HA-binding face of the folded protein in an i, i+4, i+7 motif. This motif was used to design two HA-binding peptides with high helicity and monomeric structure.

Based on the folding propensity of control peptides containing glutamic acid (Glu) in place of the Gla residues, the 36-residue peptide, JAK1, was favored. JAK1 displayed calcium-induced helical folding, which was similar to that observed for osteocalcin. Circular dichroism showed that JAK1 bound to HA as a helix, reversibly unfolded, and desorbed from HA at high temperatures. This is the first de novo designed peptide to fold in a surface-induced manner and the first circular dichroism method capable of examining peptide structure HA-particles.

Surface binding was characterized by X-ray photoelectron spectroscopy (XPS), absolute coverage, and binding affinity. These studies showed that JAK1 coverage was nearly quantitative and Gla-dependent. The affinity of JAK1 was nearly twice that of BSA and the dissociation constant was similar to that of osteocalcin.

The force of the Gla-calcium interaction was directly measured using an atomic force microscope (AFM). Model pentapeptides, α-helices, and proteins all showed greater bond-rupture forces when Gla residues were used in place of Glu residues. This study showed that the bond-rupture force associated with osteocalcin was higher than that of BSA, which may explain its higher coverage, binding affinity, and concentration in bone.

A ligand-bound variant of JAK1 was designed, and evaluated for osteogenic potential. This study showed that surface-bound BMP2 can enhance osteogenesis at the 3-day time point. Lastly, the adsorption of an amphiphilic β-hairpin peptide to hydrophobic surfaces was characterized by showing the role of peptide folding and concentration on adsorbate structure. These studies show the feasibility of designing surface-folding peptides and outline their application towards targeted drug delivery.

Indexing (document details)
Advisor: Beebe, Thomas P., Jr.
Commitee: Johnston, Murray, Rabolt, John, Schneider, Joel
School: University of Delaware
Department: Department of Chemistry and Biochemistry
School Location: United States -- Delaware
Source: DAI-B 70/07, Dissertation Abstracts International
Source Type: DISSERTATION
Subjects: Analytical chemistry, Biochemistry, Organic chemistry, Biophysics
Keywords: Carboxyglutamic, Circular dichroism, Peptide folding, Surface folding
Publication Number: 3360285
ISBN: 9781109249323
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