In synthetic biology, microbes are often used to produce proteins from natural models. Until now, however, its use has been limited to small proteins. Scientists have now managed to overcome this obstacle and produce microbiologically very large muscle protein – titin. The spun fibers of this particle result in a particularly stable, tear-resistant and flexible material that is also produced sustainably and is biodegradable.
Some of the most unusual and powerful materials can be found in nature – from extremely strong spider threads to sea silk that sticks under water to the super rubber Resilin found in flea jumping legs, for example. Earlier attempts to technically recreate such materials did not come close to the original materials, and also did not follow natural models in terms of environmental friendliness: “Artificially produced high-performance polymers are generally not biodegradable and are obtained from crude oil thanks to energy-intensive processes with toxic solvents and by-products, writes a research team led by Christopher Bowen of Washington University in St. Louis.
Microbes as protein producers
Instead, Bowen and his colleagues took a different approach to the production of new, high-yield material: they found a method that allows genetically modified microorganisms to faithfully produce very large proteins. ‘Many small molecules are already produced sustainably with the microbes,’ write the researchers. “In contrast, the direct microbial synthesis of high-yield polymers is a challenge.”
This is because most of nature’s supermaterials are made of very large proteins. “However, they are extremely difficult to produce in microbes because the yield with such large molecules is low, and properly modified microbes are genetically unstable,” the researchers explain. To get around this, they decided to use a trick. In each case, they provided the microbes with only small stretches of large total protein and completed sites where the fragments could be joined together. In this way, they managed to produce muscle protein titin – the largest known human protein.
‘In muscle tissue, titin provides muscles with a combination of strength, cushioning capacity and quick mechanical regeneration,’ explain the researchers. In order to obtain similar properties with the titanium produced by microorganisms, they stretch proteins into fibers. To do this, they first destroyed the three-dimensional structure of the proteins with a denaturing solution. They pressed the thus developed proteins into the water through a fine-mesh needle so that the individual titin molecules fused together to form fibers during refolding. “Regular, cylindrical filaments did form,” the researchers say.
At ten microns in diameter, these fibers are ten times thinner than a human hair. According to scientists, about 250 meters of titanium fibers can be obtained from one liter of microbial culture. The researchers then checked whether the fibers made of the microbes actually had the desired properties of natural muscle fibers. Result: “Both the strength and elasticity of these fibers are well above the values measured for the muscle fibers and individual myofibrils,” the researchers said. “Moreover, these strength values even exceed those of many of the hardest synthetic and natural materials.” For example, microbiologically produced Titin is even more potent than Kevlar.
Molecular analyzes confirmed that this exceptional resistance is in fact due to a structure composed of particularly large proteins. “This underlines the value of the new large polymer production strategy,” write Bowen and his colleagues. According to the researchers, other large proteins can also be made using the new technology. “The beauty of this system is that it is a platform that can be deployed anywhere,” says Bowen’s colleague Cameron Sargent. “We can take proteins from different natural contexts and then plug them into this polymerization platform and produce larger, longer proteins for different material applications with greater durability.”
Scientists believe that artificial titin has many potential uses. Like Kevlar, it can be used in, for example, bulletproof vests, but also for biomedical purposes. Since it is almost identical to the proteins found in muscle tissue, it is likely to be biocompatible and can therefore be used, for example, for surgical sutures.
Source: Christopher Bowen (Washington University in St. Louis, USA) et al., Nature Comminications, doi: 10.1038 / s41467-021-25360-6