Types of Recombinant Drugs - Biotechnology and Your Health: Pharmaceutical Applications - page 50

One more trick allowed scientists to control when the insulin
pieces would be produced. Both enzyme-insulin chain DNA cas-
settes included a promoter that would trigger the production of the
fused proteins when a simple chemical was added to the bacteria.
When the bacteria had grown to a high concentration in the vat, the
chemical was added to trigger the production of both enzyme-
insulin chain fusion proteins. The mixtures of the two proteins are
purified and treated to clip off the enzyme protein from both
insulin chains. The liberated chains join together through the weak
chemical bonds and take the shape of insulin. Yeast have also been
genetically engineered to produce human insulin.
The Shape of Proteins
In this business, size and shape are critical. Most proteins, like
insulin, will only have the right effect on cells if they have the correct
sequence of amino acids and the appropriate three-dimensional
shape. This is because, in order to work, the protein must fit neatly
and precisely into the pocket of another protein, called its receptor .
Insulin has effects on various cells because those cells have a docking
protein for insulin—the insulin receptor—on their outer mem-
branes. The receptor is connected inside the cell with biochemical
“toggle switches” that signal that insulin has arrived. Insulin must fit
into the receptor like a key in a lock in order to cause very specific
biochemical changes in the receptor and trigger its effect. The
wrong key works poorly, if at all (Figure 4.3).
There are thousands of sets of signal proteins, like insulin and
its receptor. These systems of paired protein-control molecules
and their receptors have evolved over millions of years and
provide the very precise orchestration of thousands of different
chemical reactions that are required to keep our bodies alive and
working. Although illness that develops because of a failure in
these systems may seem like a terrible betrayal of how things
should work, the fact that so many complex systems in so many