Crystal structure of CmnB involved in the biosynthesis of the nonproteinogenic amino acid l-2,3-diaminopropionic acid

l-2,3-Diaminopropionic acid (l-Dap) is a nonproteinogenic amino acid that plays as an important role as a building block in the biosynthesis of several natural products, including capreomycin, viomycin, zwittermicin, staphyloferrin and dapdiamide. A previous study reported that CmnB and CmnK are two enzymes that are involved in the formation of l-Dap in the biosynthesis of capreomycin. CmnB catalyzes the condensation reaction of O-phospho-l-serine and l-glutamic acid to generate N-(1-amino-1-carboxyl-2-ethyl)glutamic acid, which subsequently undergoes oxidative hydrolysis via CmnK to generate the product l-Dap. Here, the crystal structure of CmnB in complex with the reaction intermediate PLP-α-aminoacrylate is reported at 2.2 Å resolution. Notably, CmnB is the second known example of a PLP-dependent enzyme that forms a monomeric structure in crystal packing. The crystal structure of CmnB also provides insights into the catalytic mechanism of the enzyme and supports the biosynthetic pathway of l-Dap reported in previous studies.