Crystallization and preliminary X-ray crystallographic analysis of the catalytic domain of pyrrolysyl-tRNA synthetase from the methanogenic archaeon Methanosarcina mazei.

Pyrrolysyl-tRNA synthetase (PylRS) from Methanosarcina mazei was overexpressed in an N-terminally truncated form PylRS(c270) in Escherichia coli, purified to homogeneity and crystallized by the hanging-drop vapour-diffusion method using polyethylene glycol as a precipitant. The native PylRS(c270) crystals in complex with an ATP analogue belonged to space group P6(4), with unit-cell parameters a = b = 104.88, c = 70.43 A, alpha = beta = 90, gamma = 120 degrees , and diffracted to 1.9 A resolution. The asymmetric unit contains one molecule of PylRS(c270). Selenomethionine-substituted protein crystals were prepared in order to solve the structure by the MAD phasing method.