Purification, crystallization and preliminary crystallographic studies of plant S ‐adenosyl‐ l ‐homocysteine hydrolase ( Lupinus luteus )

By degrading S ‐adenosyl‐ l ‐homocysteine, which is a byproduct of S ‐adenosyl‐ l ‐methionine‐dependent methylation reactions, S ‐adenosyl‐ l ‐homocysteine hydrolase (SAHase) acts as a regulator of cellular methylation processes. S ‐Adenosyl‐ l ‐homocysteine hydrolase from the leguminose plant yellow lupin ( Lupinus luteus ), LlSAHase, which is composed of 485 amino acids and has a molecular weight of 55 kDa, has been cloned, expressed in Escherichia coli and purified. Crystals of LlSAHase in complex with adenosine were obtained by the hanging‐drop vapour‐diffusion method using 20%( w / v ) PEG 4000 and 10%( v / v ) 2‐propanol as precipitants in 0.1  M Tris–HCl buffer pH 8.0. The crystals were tetragonal, space group P 4 3 2 1 2, with unit‐cell parameters a = 122.4, c = 126.5 Å and contained two protein molecules in the asymmetric unit, corresponding to the functional dimeric form of the enzyme. Atomic resolution (1.17 Å) X‐ray diffraction data have been collected using synchrotron radiation.