The penultimate step in the pathway of riboflavin biosynthesis is catalyzed by the enzyme
lumazine synthase (LS). One of the most distinctive characteristics of this enzyme is the
structural quaternary divergence found in different species. The protein exists as pentameric
and icosahedral forms, built from practically the same structural monomeric unit. The
pentameric structure is formed by five 18-kDa monomers, each extensively contacting
neighboring monomers. The icosahedrical structure consists of 60 LS monomers arranged …