Natural Ribosomally Synthesized Circular Proteins

Over recent years several examples of natural ribosomally synthesized circular proteins from a diverse range of organisms have been discovered. They are special molecules, whose precursors must be posttranslationally modified to join the N to C termini with a head-to-tail peptide bond. This feature appears to have a range of potential advantages over their linear counterparts, since they are less susceptible to proteolytic cleavage and show enhanced stability. The advantages of circularization are reflected by the fact that a significant number of macrocyclic natural products have found pharmaceutical applications. In this article we review the function, structure and biosynthesis of currently known circular proteins, which are produced by microorganisms, plants and animals.