Preliminary structural studies on the MtxX protein from Methanococcus jannaschii

Methanococcus jannaschii has an mtr gene cluster expressing N 5 ‐methyltetrahydromethanopterin:coenzyme M methyltransferase, which generates methane by reducing CO 2 with H 2 with concomitant energy production under strictly anaerobic conditions. Some methanogenic archaea also have an mtr gene‐cluster homologue, the mtxXAH gene cluster. M. jannaschii has both an entire mtr gene cluster and a single mtxX gene instead of the whole mtxXAH gene cluster. A PSI‐BLAST search, secondary‐structure prediction and the absence of phosphotransacetylase activity in M. jannaschii strongly support the possibility that the MtxX protein constitutes a unique methyltransferase family. In this study, the MtxX protein from M. jannaschii has been cloned, expressed, purified and crystallized. Synchrotron data were collected to 2.9 Å from a crystal of selenomethionine‐substituted MtxX protein. The crystal belonged to the primitive hexagonal space group P 6 1 22, with unit‐cell parameters a = 54.9, b  = 54.9, c = 341.1 Å, β = 120.0°. A full structure determination is under way in order to provide insight into the structure–function relationship of this protein.