Crystallization and Preliminary X-ray Diffraction of a Halophilic Archaeal Malate Synthase

Malate synthases found in cells of the halophilic Archaea constitute a third isoform of this important metabolic enzyme, in addition to the well characterized A and G isoforms. They share little sequence similarity with these other two isoforms. Database searches using basic local alignments reveal relationships between isoforms A and G, but do not indicate a significant sequence relationship between members of this third isoform and those of isoform G, and only a distant relationship with members of isoform A. This third isoform, which we propose to call isoform H (Halophilic archaeal), is also significantly smaller in size: ~100 residues shorter than isoform A, and ~300 residues shorter than isoform G. Representatives of both isoform A and G have been structurally characterized, but no three-dimensional structural information exists for isoform H. Here we report the crystallization and preliminary X-ray diffraction from a crystal form of an H-isoform member, the malate synthase from the halophilic archaeon Haloferax volcanii, originally isolated from the mud of the Dead Sea. This crystal form diffracts well, and is amenable to single crystal X-ray analysis.