Massachusetts Institute of Technology Postdoctoral physics fellow, Peter Virnau, said they have discovered the most complicated knot ever seen in a protein. The lead investigator of the study said the discovery might be linked to the protein's function as a rescue agent for proteins marked for destruction. "In proteins, the three-dimensional structure is very important to the function, and this is just one example," Virnau said. Knots are rare in proteins -- fewer than 1 percent of all proteins have any knots and most are fairly simple. The researchers analyzed 32,853 proteins, using a computational technique never before applied to proteins at this scale. Of those that had knots, all were enzymes, the researchers said, with most having a simple three-crossing, or trefoil knot; a few had four crossings; and the most complicated, a five-crossing knot, was initially found in only one protein -- ubiquitin hydrolase. The scientists said that complex knot may hold some protective value for ubiquitin hydrolase, whose function is to rescue other proteins from being destroyed -- a dangerous job. A paper on the work appears in the Sept. 15 issue of the Public Library of Science, Computational Biology.