Illustration showing the quaternary structure of the enzyme legumain. The quaternary structure is the final three dimensional shape of a protein that is made from two or more polypeptide chains. Legumain has two chains an A chain (green and orange) and a B chain (red and yellow). Alpha helices (green and red) and beta pleated sheets (orange and yellow) are secondary structures formed from the protein's polypeptide chain of amino acids. Legumain processes proteins. In plants it processes proteins in storage vacuoles and in human it generates antigens for major histocompatibility complex (MHC) molecules to present to immune system cells.