Polio Virus Structure Revealed : Scripps Team’s Discovery May Lead to Safer Vaccine
The molecular structure of the polio virus has been determined by a team of scientists led by members of the Research Institute of Scripps Clinic here.
The finding, made public today, is expected to yield major benefits both in helping make a safer vaccine for polio--still a scourge ravaging half a million people annually worldwide--as well as helping to break the codes of other poorly understood viruses, such as hepatitis A. It is the second announcement within two weeks by American scientists concerning the successful deciphering of a major virus.
Molecular biologists James M. Hogle and David J. Filman of Scripps and biologist Marie Chow of the Massachusetts Institute of Technology published their findings in Science magazine. The research was partially funded by the National Institutes of Health in Washington and the Rockefeller Foundation in New York.
Although effective vaccines against polio have existed since 1955, scientists still do not understand fully how the virus recognizes and attacks target cells. The existence now of a three-dimensional model of the virus will give researchers a new tool to find out why, in most victims, it infects tissues within the digestive tract, leaving no long-term effects, but attacks the nerve cells in the spinal cord in a few cases, causing paralysis and sometimes death.
The new information about what the surface of the virus looks like also will allow scientists to learn about the way that altered viruses work. Those viruses are used in vaccines to induce production of antibodies without causing the illness. Scientists can now study the surfaces of altered viruses and discover how they differ from the actual virus, and learn why some altered strains occasionally revert back to the original virus and cause paralysis rather than inducing the body to produce antibodies.
Such reversion in the oral polio vaccine accounts for almost all current cases of polio in the United States, which amounts to fewer than 100 cases a year.
The new work may hasten development of a synthetic polio vaccine for use in areas such as India, where more than 200,000 people fall victim to polio each year. The existing oral (Sabin) and injected (Salk) vaccines require special care in storing and distribution, which have hindered application efforts in the Third World. A synthetic vaccine could be easier to handle.
The key to its formulation lies in using only those parts of the polio virus that actually stimulate formation of antibodies. By identifying those parts--through study of the new model--scientists can try to synthesize a vaccine. Such a vaccine would not cause paralysis in isolated cases, as the present vaccines do.
Researchers at Purdue University announced last week that they had deciphered the molecular structure of a common cold virus, known as rhinovirus-14, which could help in producing man-made defenses against it.
The rhinovirus, the polio virus and several other members of the same viral family--which include hepatitis A, and foot-and-mouth disease--are characterized by having a small core of ribonucleic acid (RNA, or genetic material) surrounded by a sphere-like structure made up of 60 copies of four proteins. The protein shell, or sphere, has the symmetry of a 20-sided structure.
Pioneering work on deciphering the makeup of such viruses was done at Harvard University in the mid-1970s, when scientists determined the structure of the tomato bushy stunt plant.
“What we did was to refine the technique to the particular problem we were working on,” Filman of Scripps said.
The technique used in these cases involves X-ray crystallography and computer analysis. The virus crystal is bombarded with X-rays and the images from the resulting radiation wave scattering are collected for computer analysis. The computer, in essence, functions as a lens to allow precise identification and location of the virus’ proteins.
