|
|
|
Gregory Stephanopoulos
Current Research
Our research is focused on Metabolic Engineering, the improvement of cellular
properties using modern genetic tools. Metabolic Engineering encompasses two important
components, the modification of cellular pathways and the rigorous evaluation
of the phenotype of the resulting cells. Through examination of many cell variants
and specific genetic backgrounds, Metabolic Engineering attempts to relate the
genotype with cell function and properties. In this sense, it has been at the
forefront of the current activity of Functional or Physiological Genomics, although
it is not broadly recognized as such. There are many industrial and medical applications
of Metabolic Engineering. In recent years our group has investigated the following
topics:
Amino acid biosynthesis in Corynebacterium glutamicum: Specifically, we
have studied flux control in the lysine producing pathway and improved specific
lysine productivity through genetic and fermentation controls.
Indene bioconversion in Rhodococcus sp.: This organism possesses a rich
spectrum of enzymatic activities catalyzing oxygenation and dehydrogenation reactions
of high chiral specificity. One product of indene bioconversion is a precursor
in the manufacturing of the AIDS drug Crixivan which, however, is formed along
with other byproducts. This study examines ways to increase the yield and selectivity
of this product through analysis and specific modifications of the indene bioconversion
network.
CO2 fixation and product synthesis by the photosynthetic cyanobacterium Synechocystis
PCC 6806: This organism is an excellent model of higher plant biochemistry,
has high plasticity and relative ease of transfrormation, has fully sequenced
genome and provides an excellent platform for small molecule and biopolymer production
while reducing atmospheric carbon dioxide.
Elucidating type II diabetes by linking the expression and metabolic phenotypes
of hepatoma and hepatocyte cells: Plasma glucose accumulation can be the end
result of a multitude of biochemical paths and mechanisms initiated by a disruption
in the insulin signaling pathway. This project attempts to elucidate the relative
extent of possible glucose accumulation pathways and link such pathways to the
cellular transcriptional state measured by DNA microarrays.
To accomplish the goals of Metabolic Engineering and facilitate progress in the
above projects, we make use of a diverse array of tools as listed below:
Intracellular flux determination: Intracellular fluxes are a fundamental
determinant of cell physiology and a necessary parameter in elucidating flux control
and targets for genetic modification. Fluxes are determined by material balancing,
NMR fine spectra analysis and GC-MS measurements. Issues of observability, solution
uniqueness, and measurement redundancy need to be addressed.
DNA Microarrays: DNA microarrays provide high throughput measurements of
gene expression. We have developed full genome microarrays for Synechocystis,
and partial microarrays for C. glutamicum, Escherichia coli, and mouse genomes
that we use extensively in the above studies. We are also pursuing non conventional
applications of microarrays in exploring the combinatorial diversity of genomic
and proteomic libraries.
Bioinformatics: Our group was one of the first to realize the importance
of computational tools for handling the large volume of data generated by genomics-based
and other technologies. We deployed such methods first in 1993 for the analysis
of bioprocess data. Presently our interest is concentrated in the analysis of
microarray gene expression data, isotopic tracer and flux data for the purpose
of identifying discriminatory genes and gene expression patterns and elucidating
meaningful links of importance to functional genomics.
Bioreaction network analysis: An important feature of Metabolic Engineering
is that it concerns itself with the properties of bioreaction networks in their
entirety instead of individual reactions. This integrating feature is especially
important when one is interested in flux control distribution and other systemic
properties of importance in directing pathway modification. This activity investigates
properties of reaction networks in the context of metabolic conversions as well
as signal transduction pathways.
Further
details
< back to bio
|
