A common approach to reduce the costs associated with the production of recombinant products is to have the product secreted. In the case of E. coli as a host system, common methods to secrete protein include the Sec and Tat pathways both of which secrete into the periplasm. Here, we describe a series of experiments to enhance secretion past the outer membrane using the hemolysin, Type I, secretion pathway. Supersecreting mutant cells were studied using mRNA expression profiling (Affymetrix based) and protein expression profiling (2DE-tandem mass spectrometry based) methods. We observed a systematic downregulation in the expression of amino acyl tRNA synthetases at the mRNA and protein levels in a supersecreting mutant relative to a parent. No single mutation that we are aware of would result in this phenotype. We speculate that a decrease in protein synthesis rate may lead to higher levels of product secretion. We tested this hypothesis using a several synonymous codon changes to the hemolysin product protein that slow down protein synthesis and observed a nearly 10 fold increase in productivity without any change in growth rate. We then tested this hypothesis in a variety of different products including IL-6 and DsRed and observed consistent results. The counterintuitive observation that slower protein synthesis may lead to higher productivity is a direct result of a genomics and proteomics study of cell lines and highlights the important role that these approaches can play in engineering phenotypes.

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