A high-affinity monoclonal antibody against the FLAG tag useful for G-protein-coupled receptor study.

The FLAG sequence (DYKDDDDK) is an artificial sequence widely used to detect, quantify, and purify proteins expressed as FLAG-fusion proteins. Several highly specific monoclonal antibodies for FLAG are commercially available; however, they are not always sensitive enough to detect proteins expressed at low levels and can give rise to unacceptable levels of background signal when used for immunostaining in vitro and in vivo. The current study reports the successful establishment of hybridoma cells that produce an extremely high-affinity antibody to FLAG, namely 2H8 Ab. 2H8 Ab stained FLAG-tagged G-protein-coupled receptors more strongly than commercially available antibodies in both flow cytometry and immunostaining experiments with no background staining. 2H8 was sensitive enough to detect FLAG-tagged G-protein-coupled receptors and soluble proteins in crude preparations, which could not be achieved using commercially available antibodies. Only 10 ng of 2H8 Ab was required to immunoprecipitate FLAG-tagged G-protein-coupled receptors from cell lysates. Of note, 2H8 stained FLAG-tagged BLT2, a low-affinity leukotriene B4 receptor, expressed in vivo in the small intestine of mice under control of the villin promoter. Thus, 2H8 Ab is a promising tool for analyzing various FLAG-fusion proteins, particularly G-protein-coupled receptors, both in vitro and in vivo.