Biochemical properties and crystal structure of isocitrate lyase from Bacillus cereus ATCC 14579.

The glyoxylate cycle is an important anabolic pathway and acts under a C compound (such as acetic acid) rich condition in bacteria. The isocitrate lyase (ICL) enzyme catalyzes the first step in the glyoxylate cycle, which is the cleavage of isocitrate to glyoxylate and succinate. This enzyme is a metalo-enzyme that contains an Mg or a Mnion at the active site for enzyme catalysis. We expressed and purified ICL from Bacillus cereus (BcICL) and investigated its biochemical properties and metal usage through its enzyme activity and stability with various divalent metal ion. Based on the results, BcICL mainly utilized the Mg ion for enzyme catalysis as well as the Mn, Ni and Co ions. To elucidate its molecular mechanisms, we determined the crystal structure of BcICL at 1.79 Å. Through this structure, we analyzed a tetrameric interaction of the protein. We also determined the BcICL structure in complex with both the metal and its products, glyoxylate and succinate at 2.50 Å resolution and revealed each ligand binding modes.