Coenzyme F420-dependent methylenetetrahydromethanopterin dehydrogenase from Methanopyrus kandleri:: the selenomethionine-labelled and non-labelled enzyme crystallized in two different forms

Coenzyme F-420-dependent methylenetetrahydromethanopterin dehydrogenase (Mtd) is an enzyme involved in methanogenic energy metabolism which reversibly catalyzes the reduction of methenyltetrahydromethanopterin (methenyl-H4MPT+) to methylenetetrahydromethanopterin (methylene-H4MPT). The enzyme from the hyperthermophilic methanoarchaeon Methanopyrus kandleri could be crystallized: the non-labelled enzyme had unit-cell parameters a = 119.1, b = 151.0, c = 219.4 Angstrom and space group C222(1), while the selenomethionine-labelled enzyme had unit-cell parameters a = 119.6, b = 151.0, c = 109.9 Angstrom and also belonged to space group C222(1), indicating a surprising bisection of the c axis. The crystals grown from the non-labelled and labelled enzyme contained six and three monomers in the asymmetric unit and diffracted to about 1.9 and 1.5 Angstrom, respectively. The crystal packing of the two crystal forms seems to be similar. In particular, the crystals of the selenomethionine-labelled enzyme are highly suitable for X-ray structure determination.