Biology Reference
In-Depth Information
3
CHAPTER
Pathway Engineering as
an Enabling Synthetic
Biology Tool
Dawn T. Eriksen, Sijin Li and Huimin Zhao
University of Illinois at Urbana-Champaign, Urbana, IL, USA
INTRODUCTION
Pathway engineering has proven indispensable in the design of microbes for production
of value-added products such as drugs, biofuels, and specialty chemicals. 1 4 Typically,
a heterologous metabolic pathway producing the value-added compound is introduced into
a host microorganism. Ideally, the pathway must be efficient, producing the target
compound with high titer, yield, and productivity while balancing the metabolic burden of
the microorganism. 5 To achieve this goal, a wide variety of strategies have been developed
for pathway engineering. The following chapter will focus on the computational and
experimental tools for the design, construction, and optimization of a heterologous
metabolic pathway. Engineering of a recombinant microorganism capable of producing a
target compound with high titer, yield, and productivity is certainly not limited to the
optimization of the heterologous metabolic pathway. However, methods for engineering the
host microorganism are beyond the scope of this chapter. For further information on
metabolic engineering of the host microorganism itself, see Chapter 12. For additional
examples of the applications of pathway engineering tools for biofuels production, see
Chapter 11, and for drug discovery, see Chapter 10.
43
There are many challenges in pathway engineering. For example, one major challenge is in the
design of the pathway, which may require sorting through thousands of possible enzymes
and reactions wherein all the parameters have different substrate preferences and kinetic
features. Computational algorithms have proven vital in pathway design and have the ability
to discover novel pathways by combining enzymes from various sources to produce
nonnatural products. Another major challenge is the development of efficient and reliable
tools for pathway construction. The pathway of interest may contain many structural and
regulatory genes with sizes ranging from tens to hundreds of kilobases. Thus it is imperative
that the pathway can be readily constructed with high efficiency and fidelity.
However, pathway engineering is more than just recruiting various enzymes and stringing
them together. 6 In early recombinant gene expression studies, it was discovered that there
was significant growth inhibition in cells overexpressing superfluous genes. This inhibition
was attributed to the competition of protein synthesis machinery for essential proteins
required for cell growth versus the production of the overexpressed proteins, and the
 
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