AB Biosciences aims to provide to the research community top-notched protein reagents. These proteins are produced by human 293T-based cell lines stably transfected with proprietary mammalian expression plasmids, that are designed to express the proteins as soluble secreted products from the transfected cells. Each protein is tagged with either a His-Flag dual tag or is fused with immuno-globulin Fc domain at either the N- or the C-terminus of the protein depending upon the compatibility of such heterologous sequences locating at the either end of the protein. To facilitate efficient transportation to the extracellular compartment, the mature peptide sequences of the proteins are fused to a proprietary signal peptide at the N-terminus.
All proteins are affinity purified from the cultured media, size fractionated by SEC column chromatography under low endotoxin conditions, buffer-exchanged into physiological buffer, and stored at -80ºC. The biological activity of each protein is validated by ELISA and/or FACS analysis for the respective ligand/receptor interaction.
The SDS-PAGE image of individual lot of purified protein is included in the product information forms. The oligomeric structure, when applicable, is provided based on the molecular weight estimated in reference to the standard MW markers. Unless otherwise noted, all proteins carry the wild type amino acid sequences encoded by the genes whose Genebank accession numbers are indicated. The protein concentration is determined using the extinction coefficient calculated based on the predicted mature protein sequence using ProtoParam tool (http://www.expasy.ch/tools/protparam.html).
Our initial effort in providing such high quality protein reagents focuses on the soluble proteins of TNF (tumor necrosis factor) ligand/TNF receptor family and a panel of co-stimulator molecules. Interactions between TNF ligand and TNF receptor family proteins are central to the primary and adaptive responses as well as the long term maintenance of immune system. Interestingly, despite the divergence in their functions, members of the TNF ligand and receptor families share homologous structures and their mode of interaction is evolutionarily conserved. The majority of the TNF and TNFR family proteins are expressed as membrane proteins and can be shed as soluble proteins via cleavage by proteases. Releasing of these proteins has been shown to be indicative of the progression of various patho-physiological conditions and to be excellent candidates for biomarkers. Co-stimulatory ligands and receptors trigger the signaling pathways that are responsible for modulating the polarity, intensity, and the time course of the immune responses. For example, B7 is a co-stimulatory ligand expressed on the surface of antigen presenting cells (APC). By engaging the CD28, B7 sends a second signal to antigen-activated T cells and prevents the latter from becoming anergized or committed to programmed cell death.