Glutathione-dependent methylglyoxal detoxification (glyoxalase system)

A two-reaction, glutathione-dependent detoxification module found in bacteria and eukaryotes. Glyoxalase I converts the methylglyoxal-glutathione hemithioacetal, which forms spontaneously, to (R)-S-lactoylglutathione, and glyoxalase II hydrolyses that thioester to D-lactate while regenerating glutathione. Each reaction is carried out by more than one enzyme lineage. Glyoxalase I comes in a Zn2+-activated class (eukaryotic GLO1 and some bacterial GloA) and a Ni2+-activated class typical of bacteria (E. coli GloA), in separate PANTHER families. Glyoxalase II is carried out by non-orthologous metallo-beta-lactamase-fold enzymes in bacteria (GloB) and eukaryotes (HAGH/GLO2), and eukaryotes have both cytosolic and mitochondrial-matrix glyoxalase II, made from separate genes in budding yeast and from one alternatively initiated gene in vertebrates. Glutathione biosynthesis, methylglyoxal generation, glutathione-independent routes (glyoxalase III, methylglyoxal reductases) and downstream D-lactate oxidation are separate modules.

The non-enzymatic formation of the methylglyoxal-glutathione hemithioacetal is treated as input context rather than a protein-catalyzed part. GshA/GshB glutathione supply and D-lactate oxidation are satisfiability dependencies, not nominal parts. Dedicated methylglyoxal synthesis and glutathione-independent detoxification routes are outside this module. Target-specific candidates and exclusions belong in project batch pages; the PSEPK assessment is recorded in file:projects/P_PUTIDA/batches/ppu00620_methylglyoxal_detoxification.md. ALIGN (YeastPathways project, 2026-10): the P. putida-centred module was widened to bacteria plus eukaryotes. Glyoxalase I gained S. cerevisiae GLO1, S. pombe glo1 and human GLO1, all in PTHR10374:SF30 with the bacterial exemplars. Glyoxalase II became a ONE_OR_MORE variant set because eukaryotic GLO2/HAGH (PTHR11935) and bacterial GloB (PTHR43705:SF1) are different PANTHER families, and because S. cerevisiae has a cytosolic (GLO2) and a glycerol-induced mitochondrial-matrix (GLO4) isozyme (PMID:9261170). YeastCyc gene assignments for PWY-901 are correct. GO-CAM disagreements: the SGD model places GLO4 in cytosol; the PomBase model includes glutathione-independent glyoxalase III (hsp3101-hsp3105; budding-yeast HSP31 family), methylglyoxal reductase and lactate/lactaldehyde dehydrogenases, which are outside this module. ALIGN (methylglyoxal module completion, 2026-11): the module was made species-neutral, with KT2440 kept as one exemplar. Glyoxalase I became a ONE_OR_MORE variant set by metal-activation class, because E. coli GloA (Ni2+ class) is in PANTHER PTHR46036, not PTHR10374, and P. aeruginosa carries both classes (PMID:17513180). The Ni2+-class annoton asserts subfamily PTHR46036:SF5 because the parent family also contains plant GLX1 and uncharacterised VOC-domain subfamilies. E. coli GloB (PAINT seed of PTN002463577) and P. aeruginosa GloA3 were added as experimentally characterised exemplars. The PANTHER/PTN grounding pass asserted PTHR11935 with PAINT node PTN000232795 for eukaryotic glyoxalase II; the node is kept, but the family term is narrowed to subfamilies because PTHR11935 is HETEROGENEOUS (PNKD has diverged, HAGHL is untested) and its family review restricts GO:0004416 to SF80 and SF94, which a family-level grounding would not respect (module validator FAMILY_SCOPE_RESTRICTED). Eukaryotic glyoxalase II is therefore split into fungal cytosolic GLO2 (SF94), fungal mitochondrial GLO4 (gene product, also SF94) and vertebrate HAGH (SF80), whose single gene supplies both the cytosolic and the mitochondrial-matrix enzyme. PAINT node PTN000232795 is recorded on the HAGH annoton only: its yeast seeds (GLO2, GLO4) are listed by SGD id, so the module validator cannot match them to the UniProt exemplars of the GLO2 annoton, although the S. pombe enzymes receive their GO:0004416 IBA from it. Not modelled: E. coli GloC (YcbL), an accessory glyoxalase II in another metallo-beta-lactamase family (PMID:25670698), and plant glyoxalase I/II paralogs; they are candidates for further variants once their families are reviewed. Remaining validator note: the PTN000043163 and PTN000232795 node assessments are UNRESOLVED or NEEDS_PRUNING in the family reviews for branches outside the exemplars, which does not affect the exemplars used here.