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The completion of the human genome project has ushered in a new era of life science (1,2) in which the new challenge is to understand functions of the entire collection of the gene products, or the proteome. One important feature of biological research in this post-genomics era is the emphasis on understanding how individual components of a proteome interact with one another temporally and spatially to constitute a living organism. Over the past decade, researchers have developed various methods designed to study protein-protein interactions including displaying proteins and peptides on live microorganisms, the most well-known example being the display of random peptide libraries on filamentous phage (3,4). Many people (including the authors) have explored the use of E. coli as an alternative organism for protein and peptide display (5). Based on our expertise and experience with both flagellin (6) and thioredoxin (7), we developed FLITRX technology, a unique system that displays conformation-constrained random peptides on the bacterial surface as functional fusions between flagellin and thioredoxin (8). [ABSTRACT FROM AUTHOR]

Escherichia coli has traditionally been a popular host for the production of heterologous proteins because of its ease of genetic manipulation and growth. Recombinant proteins produced in E. coli have been useful for a variety of purposes, including the study of protein tertiary structure, structure-function experiments, enzymology, and as bio-pharmaceuticals. Despite an impressive body of literature describing the production of numerous non-native proteins in E. coli, successful results are in no way assured. The use of E. coli as a robust expression system has been hampered by several integral pitfalls. Low or undetectable expression levels can often be caused by inefficient translation initiation of eukaryotic mRNAs on bacterial ribosomes (1). Recombinant proteins produced in E. coli sometimes retain the N-terminal initiator methionine residue, as they may be a poor substrate for the host methionine aminopeptidase (2). In addition, individual purification schemes must be devised for each native recombinant protein produced in E. coli. But perhaps most importantly, it is very common for recombinant proteins expressed in E. coli to form insoluble, misfolded cytoplasmic complexes known as "inclusion bodies" (3). The likelihood of inclusion body formation is unpredictable but appears to increase in proportion to the size and complexity of the protein. [ABSTRACT FROM AUTHOR]