Supramolecular assemblies of proteins in the galleries of alpha-zirconium phosphonates

Date of Completion

January 2001

Keywords

Chemistry, Biochemistry|Biophysics, General

Degree

Ph.D.

Abstract

Understanding the role of surface functions in promoting the structure, activities, and thermal stabilities of immobilized proteins and enzymes is important in the area of biotechnology and for assessing structure-function relationships. The applications of enzymes in biotechnology and organic chemistry are growing but a fundamental basis for the role of the surface groups in directing the protein structure and function is lacking. In an attempt to characterize the role of protein-surface interactions in promoting the physical and catalytic properties of immobilized enzymes, this work focuses on the intercalation of several proteins (myoglobin (Mb), hemoglobin (Hb), lysozyme (Lys), chymotrypsin (CHT), glucose oxidase (GO), cytochrome c (Cyt c), and horseradish peroxidase (HRP) in the galleries of layered Zr(IV) metal phosphonates (α-ZrRP). The binding of the proteins in the α-ZrRP galleries was investigated by varying the surface functions from hydroxyl (α-Zr(HPO 4)2.2H2O, α-ZrP) to acetate (α-Zr(O 3PCH2COOH)2.nH2O, α-ZrCMP) and propionate (α-Zr(O3PCH2CH2COOH) 2.nH2O, α-ZrCEP). Whereas in α-ZrP the OH group is orthogonal to the layer planes, in α-ZrCMP, the OH of the carboxylate groups is oriented parallel to the matrix plane and in α-ZrCEP the OH group is oriented weakly. ^ Protein intercalation in the α-ZrP galleries was the most favorable with binding constants in the order of 104–10 7/M and stoichiometries in the range of 250 to 1400 (phosphates per protein). The protein size (tertiary structures) and conformations (secondary structures) were retained as evidenced from the diffraction and spectroscopic studies. The substrate selectivities of Mb/α-ZrP were altered in the galleries whereas Hb/α-ZrP Cyt c/α-ZrP, and HRP/α-ZrP, exhibited unusual activity and stability at 100°C. Enhanced selectivities of Hb/α-ZrP for metal complexes was indicated in thermal cleavage and gel electrophoresis studies. The surface functions of α-ZrCMP and α-ZrCEP, however, directed the renaturation of Hb and GO whereas α-ZrP did not. H-bonding and interlayer amidation reactions between the proteins and the α-ZrRP matrix were critical factors in promoting efficient protein folding. ^ Adjunct studies conducted with metal ion fluorophores and dyes exemplified the effect of the α-ZrRP surface functions in directing self-assembly in the galleries. Energy transfer efficiencies between Fl/RhB in SAZrP were ten-fold greater than in solution whereas artificial antenna effects were observed in the UO22+/Eu3+/α-ZrCEP composites. The advantages of intercalation of the fluorophores in the α-ZrRP galleries are critically evaluated in light of the effects of specific surface functions. ^

Link to Full Text

Share

COinS