Purification, crystallization and preliminary crystallographic analysis of the 23S rRNA methyltransferase RlmM (Cm2498) from Escherichia coli

The crystal of E. coli 23S rRNA methyltransferase RlmM in this study belongs to a new space group (P2₁) and is different from the known P3₁ or P3₁21 space groups. RlmM is an AdoMet-dependent methyltransferase that is responsible for 2′-O-methylation of C2498 in the peptidyl-transferase loop of bacterial 23S rRNA. This modification occurs before assembly of the 50S ribosomal subunit, and lack of C2498 methylation can cause a slight reduction in bacterial fitness. Here, the purification and crystallization of RlmM from Escherichia coli as well as its preliminary crystallographic analysis are presented. Cocrystallization of RlmM with AdoMet was carried out and X-ray diffraction data were collected to a resolution of 2.30 Å on beamline BL17U at the SSRF. However, electron density for AdoMet cannot be observed by comprehensive crystallographic analysis, indicating that it is not bound by RlmM during the cocrystallization process. The structure was solved by molecular replacement and refinement is in progress. The crystal contained one molecule in the asymmetric unit and belonged to space group P2₁, with unit-cell parameters a = 56.07, b = 59.38, c = 54.35 Å, β = 94.84°, which differs from the P3₁ or P3₁21 space groups of previously reported RlmM structures