DNA-cutting enzyme looks like scissors.

Restriction enzymes slice DNA, dice it, and snip it just where you'd like. But wait, there's more! One of these DNA-omatics not only cuts like a pair of scissors, it looks like one too, report researchers in the February NATURE STRUCTURAL BIOLOGY.

Molecular biologists delight in determining the structure of restriction enzymes because they tend to have unique characteristics. "There are more than 3,000 of them ... and each enzyme turns up its own surprises," says Aneel K. Aggarwal of Mount Sinai School of Medicine in New York.

He and his colleagues from Mount Sinai and New England Biolabs in Beverly, Mass., used X-ray crystallography to take molecular pictures of the restriction enzyme BglII in action. To do this they grew BglII molecules into a crystal and directed X rays at it.

The technique revealed that the enzyme's two subunits swing away from each other in a dramatic scissorslike motion. Whereas other restriction enzymes grip DNA like a pair of tongs, "this enzyme grabs it in a kind of sliding motion, so the two subunits slide past each other" like scissors' blades, says Aggarwal. After cleaving the DNA, BglII resets itself to an open position. In their work, Aggarwal and his coworkers compared BglII to BamH1, a restriction enzyme that recognizes similar DNA sequences but has the tonglike motion.

The researchers want to learn more about the mechanics of these two types of enzymes and then use such knowledge for engineering new ones. Scientists could use the resulting artificial enzymes for genetic studies, such as detecting specific mutations, says Aggarwal.