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Tinkering with nature.

Experimental efforts to direct the evolution of enzymes are of special interest both for their technological potential— for instance, protection against chemical agents or improved bioremediation—and for what they might tell us about our evolutionary history. Griffiths and Tawfik have devised an in vitro system with intriguing parallels to some conceptions of prebiotic conditions. In addition to the usual linking of nucleotide fragment (containing the genetic information undergoing mutation) and enzyme product (generating the phenotype subject to selection), they use antibodycoated microbeads that capture the readout of the enzyme. More importantly, they encapsulate each microbead in a 5-fl droplet of water emulsified in mineral oil. Compartmentalization of gene, enzyme, and product mimics surfacial and local environmental factors thought to be critical in concentrating biochemicals and in overcoming diffusion during prebiotic stages of evolution. Alas, the end result here is a reminder that natural evolution has worked well indeed, as heroic efforts to improve the catalytic efficiency (kcat/Km) of phosphotriesterase, which can inactivate soman and sarin, yield only a factor of two. — GJC