Crystallization and preliminary X-ray crystallographic studies of recombinant human betaine–homocysteine S-methyltransferase

Betaine–homocysteine S-methyltransferase (BHMT) catalyzes a reaction essential for regulation of methionine and homocysteine metabolism and the catabolism of choline in mammalian tissues. Human recombinant BHMT (MW = 45 kDa) has been crystallized by the hanging-drop vapor-diffusion method at 294 K using ethylene glycol as the precipitant. The crystals belong to the monoclinic space group C2, with unit-cell parameters a = 109.190, b = 91.319, c = 88.661 Å, β = 122.044°, and diffract to 2.9 Å resolution on a local rotating-anode X-ray source. Rotation-function analysis and the Matthews coefficient, V_M = 2.46 ų Da⁻¹, are consistent with a dimer in the asymmetric unit, suggesting that the active enzyme is a tetramer with 222 symmetry.