McbB from Marinactinospora thermotolerans is an enzyme that catalyzes the Pictet-Spengler (PS) reaction of L-tryptophan and oxaloacetaldehyde to produce the betaC scaffold of marinacarbolines. This is the C-terminal domain composed of 5 bundled alpha helices. It is weakly similar to the signal transduction histidine-protein kinase BarA from E. coli and the DNA endonuclease I-MsoI from Monomastix sp [1].

1: Structural Basis for beta-Carboline Alkaloid Production by the Microbial Homodimeric Enzyme McbB. Mori T, Hoshino S, Sahashi S, Wakimoto T, Matsui T, Morita H, Abe I; Chem Biol. 2015;22:898-906. PMID:26120001