The structural analysis of shark IgNAR antibodies reveals evolutionary principles of immunoglobulins.
Custom-tailored antibodies are regarded as promising weapons against serious illnesses. Since they can accurately recognize specific structures on the surface of viruses, bacteria or cancer cells, they are already being deployed successfully in cancer diagnostics and therapy, as well as against numerous other diseases. However, the stability of the sensitive antibodies is a decisive factor in every step, from production and storage to therapeutic application. By comparing the antibodies of sharks, which are very old from an evolutionary perspective, with those of humans, a team of researchers has discovered stabilizing mechanisms that can also be applied to optimize custom-tailored antibodies in humans.
The researchers chose the IgNAR (immunoglobulin new antigen receptor) shark antibody for their investigations. They crystallized parts of the antibody and determined their atomic structures using X-ray crystallography, comparing the segments with previously known structures of other immunoglobulins. For other antibody segments, they analyzed the structures using NMR spectroscopy. The researchers compared the structures and spatial distances with the results of X-ray diffraction measurements of natural shark antibody molecules to construct a comprehensive model of the IgNAR antibody.
An examination of the protein’s structure revealed that the Ig folding typical for antibodies had already developed over 500 million years ago, since it is also present in sharks. The researchers identified that the source of the of shark antibody stability results from an additional salt bridge between structurally important amino acid chains and a particularly large non-polar nucleus of the Ig fold in shark antibodies.
The researchers then integrated both stabilizing principles into human antibodies. They found that the combination of both principles led to a significant increase of stability of the human antibody fragments, which revealed that altered antibodies were produced in larger quantities. In the future, it is expected that researchers with this insight will enable the development of improved therapeutic and diagnostic antibodies. According to the results, the antibodies should become easier to fabricate and store, as well as remain active longer inside the human organism, allowing them to expand their full therapeutic potential.
The research was headed by Matthias J. Feige, PhD, and the professors Linda Hendershot of St. Jude Children’s Research Hospital in Memphis, TN; Michael Sattler, chair of bimolecular NMR spectroscopy at TU Muenchen and the Institute for Structural Biology at the Helmholtz Zentrum Muenchen; Michael Groll, chair of biochemistry at TU Muenchen; and Johannes Buchner, chair of biotechnology at TU Muenchen.