Structural domains comprising this superfamily share the structure of the cyclodipeptide synthase family of enzymes that use aminoacyl-tRNAs (aa-tRNAs) as substrates to synthesize the two peptide bonds of various cyclodipeptides, which are precursors of many secondary metabolites with diverse biological activities PMID:21296757,PMID:25284085. The use a ping-pong mechanism that begins with transfer of the aminoacyl moiety of the first aminoacyl tRNA onto a conserved serine, yielding an aminoacyl enzyme. Combination of structural and mutagenic studies have shown that the covalent intermediate reacts with the aminoacyl moiety of the second aminoacyl tRNA, forming a dipeptidyl enzyme together with the identification of the aminoacyl-binding sites of the aminoacyl tRNAs PMID:25284085.