Protein affinity reagents have aptly gained profound importance as capture reagents and
drugs in basic research, biotechnology, diagnostics and therapeutics. However, due to the
cost, labor and time associated with production of antibodies focus has recently changed
towards potential of peptides to act as protein affinity reagents. Affinity peptides are easy
to work with, non-immunogenic, cost effective and amenable to scale up. Even though
researchers have developed several affinity peptides, we are far from compiling library of
peptides that encompasses entire human proteome. My thesis describes high throughput
pipeline that can be used to develop and characterize affinity peptides that bind several
discrete sites on target proteins.
Chapter 2 describes optimization of cell-free protein expression using commercially
available translation systems and well-known leader sequences. Presence of internal
ribosome entry site upstream of coding region allows maximal expression in HeLa cell
lysate whereas translation enhancing elements are best suited for expression in rabbit
reticulocyte lysate and wheat germ extract. Use of optimal vector and cell lysate
combination ensures maximum protein expression of DNA libraries.
Chapter 3 describes mRNA display selection methodology for developing affinity peptides
for target proteins using large diversity DNA libraries. I demonstrate that mild denaturant
is not sufficient to increase selection pressure for up to three rounds of selection and
increasing number of selection rounds increases probability of finding affinity peptide s.
These studies enhance fundamental understanding of mRNA display and pave the way
for future optimizations to accelerate convergence of in vitro selections.
Chapter 4 describes a high throughput double membrane dot blot system to rapidly
screen, identify and characterize affinity peptides obtained from selection output. I used
dot blot to screen potential affinity peptides from large diversity of previously
uncharacterized mRNA display selection output. Further characterization of potential
peptides allowed determination of several high affinity peptides from having Kd range 150-
450 nM. Double membrane dot blot is automation amenable, easy and affordable solution
for analyzing selection output and characterizing peptides without ne ed for much
Together these projects serve as guideline for evolution of cost effective high throughput
pipeline for identification and characterization of affinity peptides.