Corralling Llama Antibodies For Small Molecules

Along with a nasty reputation for being spitters, llamas have another unusual feature: They produce a type of antibody that lacks a light chain. Scientists think that these simple antibodies could be useful tools in the lab and clinic because they’re easier to produce and more resistant to heat than conventional antibodies. But so far, these so-called single-domain antibodies have proven useful for detecting only large molecules like proteins. Now, for the first time, researchers have isolated high-affinity single-domain antibodies that recognize a small molecule, the potential endocrine disrupter triclocarban (Anal. Chem., DOI: 10.1021/ac201824z).

“Conventional antibodies are usually better at recognizing small molecules because their heavy and light chains create a deep binding pocket,” says Gualberto Gonzalez-Sapienza, an immunologist at the University of the Republic, in Uruguay. But he wanted to find a way to screen for single-domain antibodies that could bind small molecules like drugs, environmental contaminants, and explosives. The researchers chose to start with triclocarban, an antibacterial compound used in soaps and linked to endocrine disruption in animals.

When they immunized llamas with triclocarban, the animals produced mainly conventional, two-domain antibodies. So the team tried another approach outside of the animal to pick out the rare high-affinity, single-domain antibodies.

The researchers isolated genes for single-domain antibodies from blood lymphocytes of a llama immunized with triclocarban. Then, using phage display, the scientists expressed the antibodies on the surfaces of bacteriophages and screened for the ones that bound triclocarban with the highest affinities.

The best single-domain antibodies had dissociation constants in the low-nanomolar range, similar to those of conventional antibodies for small molecules. Now the researchers want to use their method to target other environmentally relevant small molecules.