Enzymes that make sponges spiky are promising leads for new silicon-based materials, say British scientists.

In the lab, manufacturing silica involves high temperatures and pressures and strongly acidic conditions. But many types of sea sponges can produce complex silicate skeletons and spikes, or spicules, in the normal marine environment. A team from the Universities of Strathclyde and St Andrews has been investigating the enzymes that allow sponges to do this.

The team, led by Chris van der Walle and James Naismith, studied a sponge enzyme called silicatein , which is essential for silica spicule growth. They took a similar human protein, cathepsin L, and produced chimeras with different features in common with silicatein . This approach allowed them to identify the protein parts necessary for spicule growth and suggest a mechanism for the sponges' trick.

Although silicatein  can be used to grow silica structures in the lab, it is difficult to extract from sponges and difficult to produce in large quantities. The chimeras are much easier to produce, and so open up new possibilities for 'novel functional materials for applications in bioengineering or biophysics,' said van der Walle. 'Using the chimeras, it will be possible to synthesise biosilica materials from aqueous solution at neutral pH. This has obvious advantages where the intention is to immobilise or encapsulate sensitive biological molecules in silica.' 

Chris Exley, a bioinorganic chemist at Keele University, UK, points out that, despite these advancements, we are still a long way from explaining exactly how sponges work their magic without the benefit of lab conditions. Researchers study supersaturated solutions of silicic acid - solutions in which silica is already forming, says Exley, but real sponges do not need such concentrated solutions. 'To date no one has been able to demonstrate that any biomolecule initiates the condensation of an undersaturated solution of silicic acid. This is the Holy Grail of silicification chemistry - this is what diatoms and other silica-forming organisms achieve.'

Clare Boothby