Investigation of sol -gel encapsulated G -quartet forming DNA: A novel monolithic stationary phase for capillary electrochromatography and spectroscopic characterization of a glucose -binding protein.

摘要

G-quartet forming DNA is under investigation as a stationary phase in capillary electrochromatography (CEC). Separations of small molecules and proteins have previously been achieved using capillaries coated with this oligonucleotide in open-tubular capillary electrochromatography (OTCEC) [7-11]. This dissertation describes the development of a monolithic stationary phase for CEC prepared by entrapping G-quartet forming DNA in the pores of a sol-gel.;Circular dichroism (CD) and UV/visible absorbance spectroscopies were used to investigate the effects of sol-gel encapsulation on the G-quartet forming DNA. Results indicated that the oligonucleotide retains its characteristic conformation under sol-gel processing conditions. Since the free oligonucleotide was found to leach from the pores of the sol-gel, an immobilization scheme was utilized, whereby the DNA is attached to a silica microsphere via a biotin-streptavidin linkage. Both traditional tetra methoxysilane (TMOS) sol-gels and photopolymerized methacryloxypropyltrimethoxysilane (MPTMS) sol-gels were investigated for use in the monolithic stationary phases. Baseline resolution of polycyclic aromatic hydrocarbons (PAHs) was achieved using a monolithic, photopolymerized sol-gel stationary phase containing encapsulated G-quartet forming DNA immobilized on silica microspheres.;The galactose/glucose binding protein (GGBP) is reported to undergo a conformational change upon binding with glucose [63]. By labeling the protein with a fluorophore that is sensitive to its microenvironment, the conformational changes in the protein may provide a basis for glucose sensing. Towards this end, collaborators at BD Technologies prepared several mutants of GGBP that were site-specifically labeled with a nitrobenzoxadiazole (NBD) group. The fluorescence intensity of the NBD-labeled GGBP increased upon binding with glucose, to an extent that was dependent upon the position of the fluorescent label.;Fluorescence lifetime and CD measurements were used to further investigate the interactions between GGBP and glucose, both in solution and in sol-gel and alginate matrices. The CD results showed little difference in conformation among the mutants and did not reveal significant changes in the secondary structure of the protein upon binding with glucose; however, thermal denaturation studies showed some differences in the stabilities of the mutants. Fluorescence lifetimes, which are sensitive to the microenvironment of the fluorophore, indicated bi-exponential decays for the NBD-labeled proteins in all cases, suggesting the presence of two stable protein-dye conjugate conformations. Upon binding with glucose, the most significant change in fluorescence lifetime was seen in the triple mutant, which also had the largest increase in fluorescence intensity.