Development of a novel mammalian display system for selection of antibodies against membrane proteins.

Reliable, specific polyclonal and monoclonal antibodies are important tools in research and medicine. However, the discovery of antibodies against their targets in their native forms is difficult. Here, we present a novel method for discovery of antibodies against membrane proteins in their native configuration in mammalian cells. The method involves the co-expression of an antibody library in a population of mammalian cells that express the target polypeptide within a natural membrane environment on the cell surface. Cells that secrete a single-chain fragment variable (scFv) that binds to the target membrane protein thereby become self-labeled, enabling enrichment and isolation by magnetic sorting and FRET-based flow sorting. Library sizes of up to 109 variants can be screened, thus allowing campaigns of naïve scFv libraries to be selected against membrane protein antigens in a Chinese hamster ovary cell system. We validate this method by screening a synthetic naïve human scFv library against Chinese hamster ovary cells expressing the oncogenic target epithelial cell adhesion molecule and identify a panel of three novel binders to this membrane protein, one with a dissociation constant (KD ) as low as 0.8 nm We further demonstrate that the identified antibodies have utility for killing epithelial cell adhesion molecule-positive cells when used as a targeting domain on chimeric antigen receptor T cells. Thus, we provide a new tool for identifying novel antibodies that act against membrane proteins, which could catalyze the discovery of new candidates for antibody-based therapies.

First characterization of SmOPG1, a novel protein involved in gonad-associated processes in Schistosoma mansoni.

In the context of investigating the exceptional reproductive biology of schistosomes, several studies have focused on the identification and characterization of involved molecules. Among these are cellular tyrosine kinases (CTKs) which control differentiation processes in the female gonads. On the way to unravel CTK-mediated signaling processes in more detail, several upstream- and downstream partners of these CTKs were identified. In this context we present here first data characterizing the novel orphan gene Sm opg1. Annotated as hypothetical protein, SmOPG1 was identified as an interaction partner of the CTK SmTK6 by yeast two-hybrid library screening. Y2/3H interaction studies showed that SmTK6 binds with its SH2 domain to a specific binding motif within the C-terminus of SmOPG1. Additionally, in situ-hybridization and organ-specific RT-PCR analyses demonstrated the co-localization of SmOPG1 and SmTK6 transcripts in the gonads of adult S. mansoni. Finally, SmOPG1 knock-down provided first hints for a function in the ovary.

Cryptic 3' mRNA processing signals hinder the expression of Schistosoma mansoni integrins in yeast.

The expression of parasite genes has often proven difficult in heterologous systems such as yeast or E. coli. Most often, promoter choice and codon usage were hypothesised to be the main reason for expression failures. The trematode parasite Schistosoma mansoni has five integrin genes named Smα-Int1-4 and Smß-Int1, which we aimed to express in the yeast Saccharomyces cerevisiae. This has not been achieved, however, as only Smß-Int1 integrin could be expressed. When the four α integrins were driven by a stronger promoter, this enabled Smα-Int1 to be expressed as well, but the remaining integrins, Smα-Int2-4, still could not be expressed. Evidence from RT-PCR experiments suggested that this was due to premature transcription termination. Using detailed in silico sequence analyses we identified AT-rich stretches in these integrin genes, which have high similarity to yeast mRNA 3'-end processing signals. We hypothesised that these signals were causing the premature truncation. To test this, we designed an optimised version of Smα-Int3, in which the sequence was modified to replace the yeast 3' processing signals. This strategy allowed us to express Smα-Int3 integrin successfully in S. cerevisiae. These findings show that the misinterpretation of AT-rich sequences by yeast 3'-mRNA processing machinery can cause problems when attempting to express genes containing such sequences in this host.

DNA induces conformational changes in a recombinant human minichromosome maintenance complex.

ATP-dependent DNA unwinding activity has been demonstrated for recombinant archaeal homohexameric minichromosome maintenance (MCM) complexes and their yeast heterohexameric counterparts, but in higher eukaryotes such as Drosophila, MCM-associated DNA helicase activity has been observed only in the context of a co-purified Cdc45-MCM-GINS complex. Here, we describe the production of the recombinant human MCM (hMCM) complex in Escherichia coli. This protein displays ATP hydrolysis activity and is capable of unwinding duplex DNA. Using single-particle asymmetric EM reconstruction, we demonstrate that recombinant hMCM forms a hexamer that undergoes a conformational change when bound to DNA. Recombinant hMCM produced without post-translational modifications is functional in vitro and provides an important tool for biochemical reconstitution of the human replicative helicase.