A visit to a maternity hospital had a lasting impact on a biochemist from Trinity College, Dublin. It eventually led to important new discoveries about how proteins function, information that points new treatments for jaundice.
Dr Tim Mantle, lecturer in the Department of Biochemistry, went to visit his premature newborn son in maternity hospital. He was amongst a group of "bright orange" infants who, as often happens just after birth, were jaundiced.
The distinctive colouring occurs because the body is not getting rid of a yellow pigment, bilirubin. This is one of the breakdown products of haem the oxygen-carrying molecule in red blood cells.
It is essential to clear bilirubin because elevated levels are toxic and can cause damage, Dr Mantle explained. Mild cases can be cleared by exposing the person to strong light, but in severe cases an "exchange transfusion" is needed with the full replacement of the patient's blood supply.
The doctors told Dr Mantle that choosing between the treatments could be a difficult decision and that a test was needed to help them decide the level of bilirubin in the blood. "They said why don't you invent an assay to allow us to measure this more accurately."
The assay proved quite difficult but the research into the proteins associated with bilirubin has yielded much new information about how the proteins do their job.
The haem breaks down in a series of steps as it is reduced by various enzymes. An enzyme is a type of protein that acts like a catalyst to make chemical reactions take place and, like all proteins, its shape is critical to its function. If it did not adopt a particular shape it could not do its job properly.
Haem is toxic and first transforms to the blue-green pigment, biliverdin, and then to bilirubin.
The intermediate substance is not known to be toxic so learning how to block the change from biliverdin to bilirubin could offer a new way to stop the onset of jaundice, Dr Mantle explained.
He and his team isolated and cloned the gene that produces the enzyme that reduces biliverdin and studied how it works in great detail. Their work was published in the journal, Nature Structural Biology and provided important insights into the biochemistry that underlies how many proteins work.
The enzyme has two forms known as BVR-A and BVR-B. "[Type] A is a very good target for jaundice," Dr Mantle said. He describes them as "nanomachines", tiny machines which because of their shape and chemistry can drive reactions in the body.
The team found that the BVR protein has moving parts which facilitate chemical reduction. "Some elements are far more mobile than others," he explained. They worked with Prof Miguel Coll at the CSIC research institute in Barcelona who provided images of the protein using crystallography. A powerful Cray supercomputer was also used to model its chemical function.
They found that like many enzymes BVR uses a cofactor, a second substance that enables the chemical reduction to bilirubin to take place. They discovered that the cofactor, called NADPH, first docked onto the enzyme's surface and was locked into place by two moveable "arms" on the enzyme.
Together the enzyme and NADPH form a "pocket" where in turn the biliverdin will fit like a key into a lock. When in position the NADPH transfers across a hydride to the biliverdin which converts it to bilirubin and releases it from the enzyme pocket.
"Having a picture of the target is fantastic because it gives us an idea of what might fit in these pockets," Dr Mantle said. It offers researchers a way to identify potential new drug treatments on the basis of a drug molecule's shape. It also gives the precise molecular steps needed to achieve biliverdin reduction.