Expression, crystallization and preliminary X-ray analysis of McbB, a multifunctional enzyme involved in β-carboline skeleton biosynthesis.

β-Carboline alkaloids (βCs), with tricyclic pyrido[3,4-b]indole rings, have important pharmacological and therapeutic value. In the biosynthesis of βCs, the Pictet-Spengler (PS) cyclization reaction is responsible for the formation of ring structures. McbB is one of a few enzymes that are known to catalyse PS cyclization. It can also catalyse decarboxylation and oxidation. Here, the expression, crystallization and preliminary data analysis of McbB are reported. The crystals diffracted to 2.10 Å resolution and belonged to the monoclinic space group P21, with unit-cell parameters a = 66.06, b = 85.48, c = 106.19 Å, α = 90.00, β = 106.77, γ = 90.00°. These results provide a basis for solving the crystal structure and elucidating the catalytic mechanism for McbB.