Illustration of a monellin protein that has been engineered to promote domain swapping. Domain swapping is a process where two or more identical polypeptide chains, the simplest structure of a protein, exchange structural elements. The gene for this protein has been mutated so that a loop between two of the protein's beta-strands is deleted. This has lead to domain swapping in a protein that does not normally undergo this process. Monellin, from the fruit of the serendipity berry (Dioscoreophyllum cumminsii), is perceived as sweet by humans.