New twist in the way a protein turns.

Each protein - a molecule critical to life - consists of a long chain of amino acids folded and twisted to give it a functional shape. In the past, researchers thought these chains could bend in only four ways. Now they know of at least one more.

Biochemists discovered the new kind of folding while examining pectate lyase C, a 353-amino-acid bacterial enzyme that causes potatoes, tomatoes, apples, and tropical plants to rot. Crystallographic studies conducted by Marilyn D. Yoder, Frances Jurnak, and Noel T. Keen at the University of California, Riverside, revealed that the amino acids spiral around to form a molecular corkscrew called a parallel beta helix.

This newly identified spiral is more compressed and its loops wider than those in an alpha helix, the twist in a typical protein, notes Fred E. Cohen of the University of California, San Francisco. It requires about 22 amino acids per turn, compared with the alpha helix's 3.6 amino acids per turn. Other loops extending from this spiral provide platforms for the enzyme's chemical activities, the Riverside team reports in the June 4 SCIENCE.