Leishmania infantum Glyoxalase II
Overview
The glyoxalase pathway catalyzes the formation of D-lactate from methylglyoxal, a toxic byproduct of glycolysis. In trypanosomatids, trypanothione replaces glutathione in this pathway, making it a potential drug target, since its selective inhibition might increase methylglyoxal concentration in the parasites.
Evolutionary analysis shows that trypanosomatid L. infantum glyoxalase II diverged early from eukaryotic enzymes, being unrelated to prokaryotic proteins. This enzyme shows absolute specificity towards trypanothione, making it an exceptional model to understand the molecular basis of trypanothione binding and specificity.
Leishmania infantum
Leimaniasis is a disease caused by flagellated protozoa, belonging to the Trypanosomatids family. The Trypanosomatids are the etiological agents of several human and animal diseases, widespread in the third world and in the Mediterranean basin. It is estimated that 12 million people in the World are infected with one of this disease forms and that 2 million new cases are detected per year in 88 countries. Emergent target populations for leishmaniasis are HIV patients and people following immunosupressor therapies. No curative drugs or vaccines currently exist and actual therapeutic approaches are becoming limited given their undesirable side effects and the evolution of resistant forms of trypanosomatids.
The life cycles of Leishmania infantum
involves a vertebrate host (human) and a vector (sand fly). In the vector the parasite adopts a characteristic morphological form known as the promastigote. When the vector bites the vertebrate host, promastigotes are injected and enter the host cells, where they change into a form called the amastigote.
Trypanosomatids have 2 unique characteristics: the first is the compartimentation of glycolysis in the glycosome; and the second is the functional replacement of glutathione by trypanothione and, consequently, the replacement of the gluthatione-dependent enzymes by trypanothione-dependent ones.
Trypanothione
Trypanothione is a compound produced by Trypanosomatids, formed by two glutathione molecules bound by a spermidine molecule.
The Glyoxalase Pathway
The glyoxalase system is the main detoxification pathway of methylglyoxal, which is a toxic and mutagenic byproduct of glycolysis.
The methylglyoxal reacts nonenzimatically with glutathione, forming an hemithioacetal. This is isomerised by glyoxalase I, forming the thiol-ester S-D-Lactoylglutathione, which is then hydrolysed to D-lactate and glutathione by glyoxalase II. This pathway is no exception in Trypanosomatids concerning the co-factor being Trypanothione-dependent.
In Leishmania infantum, the glyoxalase I has activity with glutathione, although it preferentially uses trypanothione. Glyoxalase II is specific to S-D-lactoyl-trypanothione, being an outstanding model to study trypanothione specificity.
The L. infantum Glyoxalase II Structure
The crystal structure of Leishmania infantum glyoxalase II (2p18) is the first structure of this enzyme from trypanosomatids. It is a 295 amino acid metalloprotein. The overall structure of Leishmania infantum glyoxalase II is very similar to its human counterpart. Like the human glx II, it is a monomer arranged in two domains and its active site is very conserved. However it shows important differences at the substrate binding site.
Full crystallographic information is available from OCA.
