How Two Scientists Took an Antibody Apart

Antibodies were once a function in search of a structure. Immunologists knew what they did, and nobody could say what they were.

In the late 1950s Rodney Porter used the enzyme papain to cleave antibodies into fragments, some of which still bound their target. Gerald Edelman took a different route, using chemistry to break the molecule's disulfide bonds and showing that it was built from more than one chain. Their results converged on the picture now in every textbook: two heavy chains and two light chains, assembled into a Y. They shared the 1972 Nobel Prize in Physiology or Medicine.

The Y has a useful division of labor. The tips of its arms vary from antibody to antibody and do the recognizing. The stem is more constant and recruits the rest of the immune system.

That modular logic is why antibodies became such adaptable medicines. Change the tips and you change the target, while the rest of the molecule keeps doing its familiar work. Engineers now fuse, trim and arm these molecules in ways their discoverers could not have planned for, and the Y is still recognizably underneath.