Depicting topology and handedness in jellyroll structures

The jellyroll structure is a special case of the Greek key topology and, to date, has only been observed in complete form in one of its four possible arrangements. Like other elements of super-secondary structure involving the beta-strand (e.g. the beta alpha beta unit) the known structure forms a right-handed superhelix. The possibility of losing such tertiary information and other problems associated with representing these structures by two-dimensional topology diagrams are discussed. A series of rules are presented which allow this three-dimensional information to be represented in two-dimensional topology diagrams from which the handedness of a jellyroll structure can be determined.