Distinct classes of glyoxalase I: metal specificity of the Yersinia pestis, Pseudomonas aeruginosa and Neisseria meningitidis enzymes.

The metalloisomerase glyoxalase I (GlxI) catalyses the conversion of methylglyoxal-glutathione hemithioacetal and related derivatives into the corresponding thioesters. In contrast with the previously characterized GlxI enzymes of Homo sapiens, Pseudomonas putida and Saccharomyces cerevisiae, we recently determined that Escherichia coli GlxI surprisingly did not display Zn2+-activation, but instead exhibited maximal activity with Ni2+. To investigate whether non-Zn2+ activation defines a distinct, previously undocumented class of GlxI enzymes, or whether the E. coli GlxI is an exception to the previously established Zn2+-activated GlxI, we have cloned and characterized the bacterial GlxI from Yersinia pestis, Pseudomonas aeruginosa and Neisseria meningitidis. The metal-activation profiles for these additional GlxIs firmly establish the existence of a non-Zn2+-dependent grouping within the general category of GlxI enzymes. This second, established class of metal activation was formerly unidentified for this metalloenzyme. Amino acid sequence comparisons indicate a more extended peptide chain in the Zn2+-dependent forms of GlxI (H. sapiens, P. putida and S. cerevisiae), compared with the GlxI enzymes of E. coli, Y. pestis, P. aeruginosa and N. meningitidis. The longer sequence is due in part to the presence of additional regions situated fairly close to the metal ligands in the Zn2+-dependent forms of the lyase. With respect to sequence alignments, these inserts may potentially contribute to defining the metal specificity of GlxI at a structural level.