Crystallization and preliminary X‐ray diffraction analysis of the interaction of Aeromonas hydrophila MtaN‐1 with S ‐adenosylhomocysteine

Prokaryotic 5′‐methylthioadenosine/ S ‐adenosylhomocysteine nucleosidase (MtaN) is a multifunctional enzyme that can hydrolyze S ‐adenosyl‐L‐homocysteine (SAH) and S ‐methyl‐5′‐thioadenosine (MTA) to give S ‐ribosyl‐L‐homocysteine (SRH) and S ‐methyl‐5′‐thioribose (MTR), respectively. This reaction plays a key role in several metabolic pathways, including biological methylation, polyamine biosynthesis, methionine recycling and bacterial quorum sensing. Structurally, MtaN belongs to the MtnN subfamily of the purine nucleoside phosphorylase (PNP)/uridine phosphorylase (UDP) phosphorylase family. Aeromonas hydrophila has two MtnN subfamily proteins: MtaN‐1, a periplasmic protein with an N‐terminal signal sequence, and MtaN‐2, a cytosolic protein. In this study, MtaN‐1 from Aeromonas hydrophila was successfully expressed and purified using Ni–NTA affinity, Q anion‐exchange and gel‐filtration chromatography. Crystals of the protein in complex with the substrate SAH were obtained and diffracted to a resolution of 1.4 Å. The crystals belonged to the trigonal space group P 3 1 21 or P 3 2 21, with unit‐cell parameters a = b = 102.7, c = 118.8 Å. The asymmetric unit contained two molecules of MtaN‐1 complexed with SAH.