Focus protein: Insulin
Regulating glucose in the blood
Proteins – as cell receptors, enzymes, hormones and pheromones – are central to communication in living things.
Insulin is a small protein hormone that signals how much of the sugar glucose there is in the blood. It has also been central to the history of protein research. It was discovered in the 1920s, and it was quickly used to treat patients with diabetes. It was the first protein to be sequenced, the first to be chemically synthesised and the first human protein to be made in engineered bacteria.
It has just 51 amino acids, arranged in two chains linked by disulphide bonds. It begins life as a much larger protein, which helps the molecule fold into the right shape. Then a large fragment of the precursor, proinsulin, is snipped free by enzymes, leaving the small, soluble hormone protein free to do its job.
People with type 1 diabetes make too little or no insulin and are treated with the hormone. People with type 2 diabetes, which most often appears in later life, have lost some degree of response to insulin. Their treatment initially focuses on diet.