Flipping the switch in the protein factory
Professor John Shine was last night named the winner of the 2010 Prime Minister’s Prize for Science, Australia’s most prestigious award for scientists.
Though currently leading the Garvan Institute of Medical Research in Sydney, next year Professor Shine will get back to his hands-on work that has yielded some of the world’s most important biotechnology discoveries.
His work was a major step in the development of human insulin to treat diabetes, and the same technology is now widely applied to the manufacture of other human proteins like blood clotting agents and hormones.
These discoveries are possible because of one significant advance in modern biotechnology- the ability to harness bacteria to produce human proteins in a petri dish.
Made up of amino acids, proteins are the building blocks for almost everything human – from our hair to our skin to our hormones, including things like insulin and adrenalin. Until Professor Shine’s work, there was no way to produce these external of the human body.
In modern biotechnology, this is now possible by inserting human DNA into bacteria, which has the unique quality of being able to rapidly produce proteins. Essentially, bacteria is used for its innate machinery, transforming it into a microscopic factory with production lines capable churning out human proteins at high speeds.
But every factory needs an ‘on switch’ and Professor Shine’s work found a way to kick start the machinery into action through a five letter genetic code – GGAGG.
Deoxyribonucleic acid, or DNA, is the genetic material that carries the code for every part of our physical existence – both physical and chemical. The translation of that code into useful proteins is a complex, multifaceted process.
One way to think of it is that DNA has the instructions to build the proteins that determine how our body looks and works. But those instructions are written in French and the builders in our cells that actually make the proteins speak English.
For a gene to be expressed (or turned on), the DNA molecule needs to be converted into Ribonucleic acid (RNA) , which acts as a translator, passing the set of instructions from the DNA into our active cells into a way they can understand. Essentially this language is expressed by four different nucleotides – adenine (A), cytosine (C), guanine (G) and uracil (U).
This RNA then forms the template for proteins to be assembled by our cellular builders, ribosomes. By reading the RNA code, the ribosome puts together the amino acids in the correct order to make the protein.
In humans, one gene on the DNA is converted to one piece of RNA which is in turn translated into one protein.
But in bacteria, one piece of RNA can be converted into many different proteins depending on where the ribosome starts building.
So how does the RNA tell the ribosome where to begin? The answer is the Shine-Dalgarno sequence – GGAGG, a start signal just before the beginning of the protein code.
This on switch was the key to starting to make human proteins in bacteria. By inserting a human gene, with the GGAGG start switch at the beginning, into bacterial DNA, scientists were able to use the bacteria to manufacture a protein such as insulin.
This was a breakthrough for diabetics, who were previously treated with insulin from pigs or cows which was in limited supply and had side effects.
But this technology is in no way restricted to making insulin, it could be applied to multiple human proteins including other hormones and enzymes like the clotting agent thrombin. In fact Professor Shine was the first scientist to use bacteria to produce a human hormone (endorphin) that was proven to be biologically active.
After many years of working with biotech companies and guiding the Garvan Institute through years of rapid growth, Professor Shine is preparing to return full time to the lab. He is setting his sights on neural stem cells, planning to explore their potential to repair the damage seen in diseases like Alzheimer’s and Parkinson’s.