We also demonstrate that co-expression of cytFkpA in the cytoplasm improves the functional protein yields of the anti-EpCAM ING1 and anti-IL1β XPA23 Fab CH5424802 fragments in the periplasm. When expressed alone, these Fabs express poorly (Table 1). Low periplasmic expression can be attributed to cell toxicity issues often resulting from poor translocation across the inner E. coli membrane and/or aggregation in the periplasm. Therefore, our

results are consistent with previous studies that showed more apparent beneficial effects of FkpA on the functional expression of toxic scFv antibody fragments ( Bothmann and Pluckthun, 2000). Interestingly, a recent study suggested that overproduction of FkpA, and to a lesser extent Skp, in E. coli enhances the viability of cells by elevating the expression of genes encoding heat-shock proteins or proteins leading to responses to misfolded protein stress ( Ow et al., 2010). It remains to be seen if the cell viability is also improved when cytFkpA is co-expressed in the bacterial cytoplasm.

The same group reported that co-production of FkpA together with Skp in the periplasm not only increases the solubility and secretion of a scFv to the extracellular medium, but also improves the cell viability. A major advantage of our approach is that the native sequences of Fabs or scFvs do not have to be altered. This approach is in contrast to previous efforts mTOR inhibitor that employ protein engineering techniques to optimize the sequence of antibody fragments by either introducing mutations to increase their solubility (i.e. by generating cysteine-free mutants allowing expression in the cytoplasm without the requirement

for refolding) (Proba et al., 1998 and Worn and Pluckthun, 1998), or by using fusion proteins (Bach et al., 2001 and Jurado et al., 2006). In conclusion, co-expression of the chaperone variant, cytFkpA, offers multiple benefits over alternative approaches for the selection of novel antibody candidates or the optimization of production of existing antibody fragments. Based on the results reported CYTH4 here, the novel expression platform we describe in this work is a useful tool for phage display and recombinant antibody manufacturing. We would like to thank Diane Wilcock for her critical reading of this manuscript. “
“Toxoplasma gondii (T. gondii) is an intracellular protozoan parasite that infects a large variety of domestic and wild mammals, including humans. In humans, infection with T. gondii is generally asymptomatic but during pregnancy, it can result in congenital infection with severe sequelae or late onset eye disease and is a frequent cause of encephalitis in severely immune suppressed patients with AIDS ( Araujo and Remington, 1987). Toxoplasmosis is also a serious complication following organ transplantation ( Aubert et al., 1996). So, detection of T.