Technology: Hunt is on for money-spinning spider gene

 作者:洪舰     |      日期:2019-02-28 03:03:03
By CHARLES ARTHUR The mystery of why spider silk is one of the strongest yet elastic materials known could soon be solved by a team of molecular biologists from the University of Wyoming. They have transferred into bacteria a DNA sequence that makes the silk protein, in order to produce larger amounts for research. At present, however, this only produces the protein in solution. The next hurdle is to determine the protein’s exact structure and to use that information to make the strong, dry form. Spider silk produced in commercial quantities would be enormously valu-able. The US Army is already ‘milking’ spiders for their silk to make bulletproof vests (Technology, 14 November 1992). It is at least twice as strong as steel, having a breaking strain of 2 109 newtons per square metre. Yet it can be stretched by more than one-third and recover without distortion. Steel only has an elasticity of 1 per cent. Kevlar, which is as strong as silk, has an elasticity of just 5 per cent. Used as a composite, like carbon fibre, silk could produce incredibly tough yet soft materials. It could also be used in medical applications, such as replacing tendons and ligaments, because it is 20 times stronger than tendon tissue and is more elastic. Like other researchers studying spider silk, the Wyoming team is struggling to come to terms with the apparently contradictory qualities of the silk protein. ‘Spiders’ webs don’t dissolve in the rain. That means that the protein is insoluble,’ says Mike Hinman, one of the researchers. ‘But in the spider it starts by being secreted from a little gland into a bulbous sac. The sac’s contents are liquid, so the protein must be soluble. Yet when the spider spins a web, the liquid is pulled down a tube towards the spinneret. It shows some liquid crystal properties there. Then it comes out as an insoluble solid. So clearly there are both chemical and physical changes going on.’ The researchers, led by Randolf Lewis, are looking for silk protein genes in species of golden orb weaver spiders, a genus which produces a particularly strong silk. They have worked out what DNA sequences are required to produce the protein, but have yet to isolate the gene that codes for it. The researchers have, however, inserted artificial genes which produce the protein into bacteria, to produce it in a soluble form. ‘It turns out to have a lot of charged amino acids at the ends. It may be that when you clip those off it becomes insoluble,’ explains Hinman. ‘The trouble is, silk is technically very hard to work with. You can’t sequence it in its natural state, because you can’t get it to dissolve.’ The team is now trying to use nuclear magnetic resonance to determine the protein structure. ‘If we get large amounts, we may be able to use other methods,’ says Hinman. ‘If we can crystallise it from the solution, we could use X-ray crystallography. ‘Really, it’s the sort of problem that was waiting for molecular biology to be invented. People have been intrigued by the exact composition of silk for 200 years. But it’s only with the development of techniques such as gene and protein sequencing in the past 10 to 15 years, that we have even been able to get close.’ The laboratory has been working on the task for the past five years,