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Capillary electrophoresis laser-induced fluorescence investigations of individual molecules of Escherichia coli β-galactosidase

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dc.contributor.supervisor Craig, Douglas (Biochemistry and Medical Genetics) en
dc.contributor.author Nichols, Ellert R
dc.date.accessioned 2009-08-20T20:46:18Z
dc.date.available 2009-08-20T20:46:18Z
dc.date.issued 2009-08-20T20:46:18Z
dc.identifier.uri http://hdl.handle.net/1993/3170
dc.description.abstract Single molecule studies of enzymes have revealed that nominally identical individual enzyme molecules are functionally heterogeneous. Different individual molecules exhibit different catalytic rates under identical conditions, and individual enzyme molecules show fluctuating rates over broad timescales. The structural basis and the biological sources for such heterogeneity remains poorly understood. Herein, studies are presented of the β-galactosidase from Escherichia coli, using capillary electrophoresis with laser-induced fluorescence (CE-LIF), to investigate the sources of catalytic heterogeneity at the single molecule level. Limited proteolysis as a possible source for single molecule heterogeneity, and for the changes in activity of a population of individual molecules over time, was investigated by inducing enzyme expression in two E.coli strains in the presence of a broad spectrum of protease inhibitors. The effect of protease inhibitors was found to be limited. β-Galactosidase was expressed from a lacZ linear template from two different E. coli strains using an in vitro protein expression system to determine if in vitro synthesized enzyme was identical to its in vivo counterpart. In vitro synthesized enzyme was found to be less active than in vivo sources. The differences were attributed to deficient N-terminal methionine removal and the higher rates of translation error associated with in vitro protein synthesis. Single molecule separations revealed that individual molecules of β-galactosidase were electrophoretically distinct, and that the electrophoretic heterogeneity was independent of source of enzyme, method of measurement, or of capillary coating. Electrophoretic modeling indicated that slight variation of hydrodynamic radius is the most likely source of electrophoretic mobility heterogeneity. The extent of single molecule catalytic variation was reduced in a mutant with a hyperaccurate translation phenotype implying that translation error is a source of the heterogeneity. Streptomycin-induced translation error reduced average activity, but did not lead to an increase in catalytic heterogeneity. No relationship between translation error and electrophoretic heterogeneity was observed. A novel CE-LIF assay was developed for the continuous monitoring of the catalytic activity and electrophoretic mobility of individual β-galactosidase molecules. Thermally-induced catalytic fluctuations were observed suggesting that individual enzyme molecules were capable of conformational fluctuations that supported different catalytic rates. en
dc.format.extent 1769936 bytes
dc.format.mimetype application/pdf
dc.language.iso en_US
dc.subject CE-LIF en
dc.subject β-galactosidase en
dc.subject Escherichia coli en
dc.subject single molecule en
dc.subject heterogeneity en
dc.subject electrophoretic mobility en
dc.title Capillary electrophoresis laser-induced fluorescence investigations of individual molecules of Escherichia coli β-galactosidase en
dc.degree.discipline Biochemistry and Medical Genetics en
dc.contributor.examiningcommittee Goltz, Doug (Chemistry) Pind, Steve (Biochemistry and Medical Genetics) Wilkins, John (Biochemistry and Medical Genetics) Arriaga, Edgar (University of Minnesota) en
dc.degree.level Doctor of Philosophy (Ph.D.) en
dc.description.note October 2009 en


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