Perfecting crystals

THE GRAVITY-FREE environment in space will form more perfect crystals of certain proteins and scientists hope that by understanding their protein structure, they will be able to design better drugs to combat diabetes and arthritis, along with some other diseases.

A protein derived from the deadly toxin found in castor beans and an AIDS virus enzyme were among the 34 protein crystals cultivated aboard the US space shuttle Columbia during its recent orbits of the earth. In the weightlessness of space, crystals grow larger and have fewer imperfections, which makes for easier analysis. Researchers can determine the structure of molecules by studying the crystal's X-ray diffraction pattern, which is the break-up of a beam of light into a series of dark or light bands. Once the structure of the crystals is known, scientists can then design different drugs, known as immunotoxins, by joining a bacterial or plant toxin to an antibody or hormone. The toxin is harmless, until it is introduced into a target cell, and the antibody or hormone binds only to specific receptors, making immunotoxins potent and selective killers.

Immunotoxins have been made from poisons derived from the diphtheria and pseudomonas bacteria and from carnations and corn. The castor bean derivative known as recombinant ricin A chain has been joined to an antibody targeted for the white blood cells known as T lymphocytes. The drug is known as CD5 and is recommended for people with acute graft-versus-host disease, which is an immune reaction that develops in patients who receive bone marrow transplants.

The results of the space experiments are eagerly awaited. The mission, according to Challenger aide Charles Bugg, principal investigator, is considered a precursor to what could be possible in a space station, which will have an entire laboratory for growing crystals.