TOPOLOGICAL CHIRALITY OF PROTEINS

A few rare instances are known in which conformational restriction on polypeptide folding patterns by disulfide cross-links results in topol ogical chirality. We now show that, once the role played by covalently bound cofactors (prosthetic groups) in conjugated proteins is taken i nto account, topological chirality is in fact more common than previou sly realized. Iron-sulfur proteins are examples of native proteins in which covalently bound Fe4S4 clusters induce topological chirality eve n in the absence of disulfide cross-links. Quinoproteins with covalent ly bound cofactors are now recognized to contain catenated substructur es, and thus provide the first example of topological complexity in a native protein. The present study strongly suggests that topological c hirality may be of wide occurrence among the diverse classes of conjug ated proteins.