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

Betaine-homocysteine S-methyltransferase (BHMT) catalyzes a reaction essent ial for regulation of methionine and homocysteine metabolism and the catabo lism of choline in mammalian tissues. Human recombinant BHMT (MW = 45 kDa) has been crystallized by the hanging-drop vapor-diffusion method at 294 K u sing ethylene glycol as the precipitant. The crystals belong to the monocli nic space group C2, with unit-cell parameters a = 109.190, b = 91.319, c = 88.661 Angstrom, beta = 122.044 degrees, and diffract to 2.9 Angstrom resol ution on a local rotating-anode X-ray source. Rotation-function analysis an d the Matthews coefficient, V-M = 2.46 Angstrom (3) Da(-1), are consistent with a dimer in the asymmetric unit, suggesting that the active enzyme is a tetramer with 222 symmetry.