By genetically altering silkworms, researchers have created silk that does not occur in nature. The results are the first industrially useful animal to be engineered to incorporate man-made amino acids.
The researchers modified the silkworms to produce silk better suited for medical applications, reports New Scientist. There are lots of groups currently exploring the use of silk in medical implants, largely because it doesn’t cause an immune reaction in the body and is already approved by many for use in a medical context.
For example, there is interest in using silk to replace knee cartilage and as a scaffolding on which organs can be grown in the lab. But while its inert properties are great when implanted into the knee, it actually comes as somewhat of a disadvantage when you want to stick cells to it, as they simply cannot adhere well.
To get around this, the researchers genetically edited the silkworms to produce silk that contains a particular amino acid not found in nature. This gives the material an anchoring point onto which cells can then stick to, and as a result make silk that is found nowhere in nature. Their results have been published in ACS Synthetic Biology.
It works because silk is simply a type of protein, all of which are made up of amino acids. The researchers managed to genetically alter the cellular machinery that translates DNA into protein to substitute 6 percent of one particular naturally occurring amino acid (in this case phenylalanine) for an artificial man-made amino acid called AzPhe.
To get the worms to make this novel silk with the new amino acid, they simply fed the insects food that contains it. The enzyme responsible for building the silk protein was then tweaked to select AzPhe instead of phenylalanine. In the earlier version of this experiment, this enzyme was woefully inefficient, but by generating thousands of gene variants for the enzyme in bacteria and then testing them, the team eventually found the most productive one.
The results have further applications than simply allowing cells to adhere. It could also be used in the dying industry, where it is quite difficult to dye natural silk and get the color to hold, and for smart medical dressings.
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