Antibody-mediated purification of co-expressed antigen-antibody complexes.

Immunoaffinity is an established chromatographic method for isolating macromolecules independently on the presence of specific tags while the tight interaction between antigen and antibody has been exploited to stabilize proteins during crystallization trials. Therefore, it seems reasonable to try to combine the two protocols, namely to co-express the target proteins together with their specific antibodies to obtain stable complexes suitable for direct purification and further analyses. Using the variable region of single domain llama antibodies, we showed that the co-expression of antigen-antibody pairs is feasible in both the periplasm and the cytoplasm of bacteria.