Methylisocitrate lyase

In enzymology, a methylisocitrate lyase (EC 4.1.3.30) is an enzyme that catalyzes the chemical reaction In enzymology, a methylisocitrate lyase (EC 4.1.3.30) is an enzyme that catalyzes the chemical reaction Hence, this enzyme has one substrate, (2S,3R)-3-hydroxybutane-1,2,3-tricarboxylate (also known as 2-methylisocitrate), and two products, pyruvate and succinate. The reaction is similar to that of isocitrate lyase, except that an additional methyl group (marked with an asterisk in the above scheme) is present, meaning that citrate is replaced by methylcitrate and glyoxylate by pyruvate. This enzyme belongs to the family of lyases, specifically the oxo-acid-lyases, which cleave carbon-carbon bonds. The systematic name of this enzyme class is (2S,3R)-3-hydroxybutane-1,2,3-tricarboxylate pyruvate-lyase (succinate-forming). Other names in common use include 2-methylisocitrate lyase, MICL, and (2S,3R)-3-hydroxybutane-1,2,3-tricarboxylate pyruvate-lyase. This enzyme participates in propanoate metabolism. Methylisocitrate lyase was discovered in 1976. As of late 2007, 6 structures have been solved for this class of enzymes, with PDB accession codes 1MUM, 1O5Q, 1OQF, 1UJQ, 1XG3, and 1XG4. The structure is very similar to that of phosphoenolpyruvate mutase. A homotetrameric biological unit is composed of beta barrels with the active site at one end. A magnesium ion is present in the active site, and an active-site 'gating loop' moves inward toward it when substrate binds and away with no substrate bound, thus shielding the reaction from solvent. Helices are present all around the beta barrels; in particular, a C-terminal helical domain splits off from the barrel to interact with the barrel of a neighboring subunit, in a 'helix swapping' motif (see phosphoenolpyruvate mutase). The following still shot from a ribbon kinemage shows one subunit from the crystal structure 1MUM, which includes a magnesium ion (gray) but no substrate; helices are red while loops are white and beta strands are green.