A major outbreak of measles in Washington State earlier this year provided a striking reminder of the infectious power of this disease, and surprising evidence that even ‘solved’ diseases like measles remain relevant in today’s world. Although effective vaccines exist, the disease persists due to limited availability in developing countries and the growing anti-vaccination movement.

In order to better understand news about disease outbreaks, it’s helpful to have some scientific context. At Nanome, we believe that people who are empowered with scientific knowledge make clearer decisions that are better for themselves and for humanity. We like to build this context from the ground up, starting with the molecules.

Proteins encoded by measles genome — the two lower proteins are both forms of measles hemagglutinin

So what molecules are behind the measles virus? Although the measles genome only encodes six proteins, it still manages to be one of the most infectious viruses known. Measles infects 9 out of 10 susceptible people exposed to it. Two of the proteins populate the surface of the measles virus: measles hemagglutinin and measles fusion protein. Hemagglutinin is the docking tool that the measles virus uses to attach itself to human cells. It is also the protein that vaccines train the human immune system to recognize and reject.

Left: single measles hemagglutinin. Right: measles hemagglutinin in dimer form, attached to human receptor protein CD46 on each side

Measles hemagglutinin is the first step in the viral hijacking process. This ‘docking tool’ is known to bind to three kinds of receptor proteins found on the surface of human cells. After docking, measles fusion proteins fuse the surfaces of the cell and the virus. Measles then releases proteins along with its viral genetic code into the cell, turning the healthy cell into a microscopic measles-producing factory.

Measles vaccines work by introducing disabled versions of the virus to your body. This trains the immune system to create proteins called antibodies. In the case of measles, these antibodies are constructed to recognize measles hemagglutinin and attach to it. This limits the functionality of the bound measles virus, and signals other immune cells to destroy the virus. For more detail on vaccines and how they work, see here and here.