A PARACHUTE made from spider silk would be incredibly strong and
light鈥攋ust pray it doesn鈥檛 rain. If it did, your chute could shrink and
you鈥檇 plunge to the ground. But now David Zax and his colleagues at Cornell
University, New York, think they are on the way towards stopping spider silk
shrinking when it gets wet.
Dragline thread, which spiders use as the main supports for their webs, is
flexible and yet stronger than steel, making it an engineer鈥檚 dream. But when
wet it can shrink to as little as 55 per cent of its original length. For a
spider this is useful鈥攐ld webs that have loosened up from wear
self-tighten when it rains. But it spells trouble for engineers. 鈥淚t鈥檚 not a
problem for seat belts unless they鈥檙e in a convertible,鈥� says Zhitong Yang at
Cornell. 鈥淏ut for a parachute, it鈥檚 definitely a problem.鈥�
The steely strength of spider silk comes from crystalline spines in the
thread. Proteins between these can swell when they get wet, forcing the
crystalline regions out of alignment and causing the thread to 鈥渟upercontract鈥�.
The group studied this effect using solid-state nuclear magnetic resonance
spectra of silk from the golden orb-weaving spider Nephila clavipes.
They found that the most probable cause of shrinkage was a repeated string of 11
amino acids. 鈥淚f it really turns out to be responsible it gives us a way to
utilise it,鈥� says Randolph Lewis, a molecular biologist at the University of
Wyoming in Laramie. 鈥淭he question is whether it will be found in all silks that
蝉耻辫别谤肠辞苍迟谤补肠迟.鈥�
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The team has suggested a structurally analogous sequence to replace the amino
acid block, making a silk that鈥檚 just as strong and elastic but not nearly as
water-sensitive. The genetic sequence coding for the block could be replaced and
the whole gene inserted into bacteria or tobacco plants for mass silk
production. 鈥淲e鈥檙e working on that,鈥� says Zax.