Scientists map structure of potent antibody against coronavirus

Scientists have shown that a potent antibody from a COVID-19 survivor interferes with a key feature on the surface of the coronavirus's distinctive spikes and induces critical pieces of those spikes to break off in the process.

The antibody -- a tiny, Y-shaped protein that is one of the body's premier weapons against pathogens including viruses -- was isolated by the Fred Hutch team from a blood sample received from a Washington state patient in the early days of the pandemic.

The research group had previously reported that, among dozens of different antibodies generated naturally by the patient, this one -- dubbed CV30 -- was 530 times more potent than any of its competitors.

Using tools derived from high-energy physics, the researches have now mapped the molecular structure of CV30.

The product of their research is a set of computer-generated 3D images that look to the untrained eye as an unruly mass of noodles. But to scientists they show the precise shapes of proteins comprising critical surface structures of antibodies, the coronavirus spike and the spike's binding site on human cells. The models depict how these structures can fit together like pieces of a 3D puzzle.

On the surface of the complex structure of the antibody is a spot on the tips of each of its floppy, Y-shaped arms. This infinitesimally small patch of molecules can neatly stretch across a spot on the coronavirus spike, a site that otherwise works like a grappling hook to grab onto a docking site on human cells.

The target for those hooks is the ACE2 receptor, a protein found on the surfaces of cells that line human lung tissues and blood vessels. But if CV30 antibodies cover those hooks, the coronavirus cannot dock easily with the ACE2 receptor. Its ability to infect cells is blunted.

This very effective antibody not only jams the business end of the coronavirus spike, it apparently causes a section of that spike, known as S1, to shear off.

The S1 protein plays a crucial role in helping the coronavirus to enter cells. Research indicates that after the spike makes initial contact with the ACE2 receptor, the S1 protein swings like a gate to help the virus fuse with the captured cell surface and slip inside. Once within a cell, the virus hijacks components of its gene and protein-making machinery to make multiple copies of itself that are ultimately released to infect other target cells.

The incredibly small size of antibodies is difficult to comprehend. These proteins are so small they would appear to swarm like mosquitos around a virus whose structure can only be seen using the most powerful of microscopes.

 

Key to building models of these nanoscale proteins is the use of X-ray crystallography. Structural biologists determine the shapes of proteins by illuminating frozen, crystalized samples of these molecules with extremely powerful X-rays. The most powerful X-rays come from a gigantic instrument known as a synchrotron light source. Born from atom-smashing experiments dating back to the 1930s, a synchrotron is a ring of massively powerful magnets that are used to accelerate a stream of electrons around a circular track at close to the speed of light. Synchrotrons are so costly that only governments can build and operate them. There are only 40 of them in the world.

See:

Nicholas K. Hurlburt, Emilie Seydoux, Yu-Hsin Wan, Venkata Viswanadh Edara, Andrew B. Stuart, Junli Feng, Mehul S. Suthar, Andrew T. McGuire, Leonidas Stamatatos, Marie Pancera. Structural basis for potent neutralization of SARS-CoV-2 and role of antibody affinity maturation. Nature Communications, 2020; 11 (1) DOI: 10.1038/s41467-020-19231-9

Posted by Dr. Tim Sandle, Pharmaceutical Microbiology Resources (http://www.pharmamicroresources.com/)