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Silica as a Matrix for Encapsulating Proteins: Surface Effects on Protein Structure Assessed by Circular Dichroism Spectroscopy
Department of Chemistry, San José State University, San José, CA 95192-0101, USA
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Received: 28 June 2012; in revised form: 20 July 2012 / Accepted: 20 July 2012 / Published: 2 August 2012
Abstract: The encapsulation of biomolecules in solid materials that retain the native properties of the molecule is a desired feature for the development of biosensors and biocatalysts. In the current study, protein entrapment in silica-based materials is explored using the sol-gel technique. This work surveys the effects of silica confinement on the structure of several model polypeptides, including apomyoglobin, copper-zinc superoxide dismutase, polyglutamine, polylysine, and type I antifreeze protein. Changes in the secondary structure of each protein following encapsulation are monitored by circular dichroism spectroscopy. In many cases, silica confinement reduces the fraction of properly-folded protein relative to solution, but addition of a secondary solute or modification of the silica surface leads to an increase in structure. Refinement of the glass surface by addition of a monosubstituted alkoxysilane during sol-gel processing is shown to be a valuable tool for testing the effects of surface chemistry on protein structure. Because silica entrapment prevents protein aggregation by isolating individual protein molecules in the pores of the glass material, one may monitor aggregation-prone polypeptides under solvent conditions that are prohibited in solution, as demonstrated with polyglutamine and a disease-related variant of superoxide dismutase.
Keywords: biocompatibility; ellipticity; ormosil; protein folding; sol-gel technique
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Calabretta, P.J.; Chancellor, M.C.; Torres, C.; Abel, G.R., , Jr.; Niehaus, C.; Birtwhistle, N.J.; Khouderchah, N.M.; Zemede, G.H.; Eggers, D.K. Silica as a Matrix for Encapsulating Proteins: Surface Effects on Protein Structure Assessed by Circular Dichroism Spectroscopy. J. Funct. Biomater. 2012, 3, 514-527.
Calabretta PJ, Chancellor MC, Torres C, Abel GR, , Jr, Niehaus C, Birtwhistle NJ, Khouderchah NM, Zemede GH, Eggers DK. Silica as a Matrix for Encapsulating Proteins: Surface Effects on Protein Structure Assessed by Circular Dichroism Spectroscopy. Journal of Functional Biomaterials. 2012; 3(3):514-527.
Calabretta, Phillip J.; Chancellor, Mitchell C.; Torres, Carlos; Abel, Gary R., , Jr.; Niehaus, Clayton; Birtwhistle, Nathan J.; Khouderchah, Nada M.; Zemede, Genet H.; Eggers, Daryl K. 2012. "Silica as a Matrix for Encapsulating Proteins: Surface Effects on Protein Structure Assessed by Circular Dichroism Spectroscopy." J. Funct. Biomater. 3, no. 3: 514-527.