Episodes of horizontal gene-transfer and gene-fusion led to co-existence of different metal-ion specific glyoxalase I

Glyoxalase pathway plays an important role in stress adaptation and many clinical disorders. The first enzyme of this pathway, glyoxalase I (GlxI), uses methylglyoxal as a substrate and requires either Ni(II)/Co(II) or Zn(II) for activity. Here we have investigated the origin of different metal ion specificities of GlxI and subsequent pattern of inheritance during evolution. Our results suggest a primitive origin of single-domain Ni dependent GlxI [Ni-GlxI]. This subsequently evolved into Zn activated GlxI [Zn-GlxI] in deltaproteobacteria. However, origin of eukaryotic Zn-GlxI is different and can be traced to GlxI from Candidatus pelagibacter and Sphingomonas. In eukaryotes GlxI has evolved as two-domain protein but the corresponding Zn form is lost in plants/higher eukaryotes. In plants gene expansion has given rise to multiple two-domain Ni-GlxI which are differentially regulated under abiotic stress conditions. Our results suggest that different forms of GlxI have evolved to help plants adapt to stress.