New Protein L Biosensor For Antibody Fragment Quantitation
Wesley McGinn-Straub, Product Manager, Fortebio
Antibodies are so rich in biochemical features that nearly every piece and parcel of their structure has been harvested and put to use, leading to widespread adoption of whole molecules, Fabs, Fvs and scFvs in both medicine and biotechnology. In conjunction with the Octet instruments, ForteBio's Protein A and Protein G biosensors have accelerated protein science research and development by enabling easy, fast and accurate quantitation of whole molecule and Fc fusion proteins. However, due to the absence of an Fc domain, — to which both Protein A and Protein G bind — detection of Fab, Fv and scFv fragments on the Octet platform has required custom biosensor preparation and validation by the end user.
ForteBio's new Protein L biosensor now brings the capability for direct detection of most kappa light chain-containing antibodies to the Octet platform, providing a reliable , time-saving "out-of-box" solution for Fab, Fv and scFv fragment quantitation. The Protein L biosensor can, of course, be used to detect whole molecule antibodies that contain kappa light chains, and may be particularly useful when the target antibody demonstrates weak affinity towards both Protein A and Protein G.
Protein L, an immunoglobulin binding protein originally isolated from Peptostreptococcus magnus, binds human kappa I, III and IV and mouse kappa I light chains of antibodies and antibody fragments. This broad specificity allows the Protein L biosensor to recognize a wider range of antibody isotypes than either Protein A or G, including IgG, IgM, IgA, IgE and IgD. Across mouse, rat and human IgG subtypes, Protein L possesses "strong" binding to nearly all species and subtypes — whereas Protein A and Protein G show "weak" or "no binding" to several species and subtypes. The Protein L biosensor is especially useful for quantifying antibodies and antibody fragments from serum–based culture because Protein L does not bind bovine immunoglobulins, which often contaminate serum supplement and thereby generate significant background signal.
As has been done for both Protein A and Protein G biosensors, standard-sensitivity and high-sensitivity acquisition parameters on the Octet platform have been developed as starting points for assay development with the Protein L biosensor. Standard sensitivity conditions (2 minute read time, 400 rpm shake speed) generated a dynamic range of 0.5–2000 µg/mL using a human IgG Fab on an Octet RED96 system. Extending the read time and increasing the shake speed (10 minute read time, 1000 rpm shake speed) produced a dynamic range of 0.05–300 µg/mL. Using the same model system, the Protein L biosensor has been shown to regenerate at least 10 times in conditioned medium with less than 5% loss in capacity, making the biosensor a cost-effective solution for screening experiments. Because the interaction of each antibody with Protein L is different, results can vary with both analyte and matrix.
The Protein L biosensor can be used for a wide variety of applications in the antibody laboratory. During cell line development, it can be used to determine the productivity of pools and individual clones. During process development, rapid determination of antibody concentration using the Protein L biosensor and the Octet platform expedites the iterative process of optimizing growth conditions and culture media. The Protein L biosensor can also be used in formulation development and quality control of biologics.
For more information, visit the Protein L biosensor web page and download the Protein L datasheet and technical note. To request a quote for Protein L biosensors, visit the ordering page.