Enzyme Structure
As of late 2007, 5 structures have been solved for this class of enzymes, with PDB accession codes 1DQU, 1F61, 1F8I, 1F8M, and 1IGW.
ICL is composed of four identical chains and requires a Mg2+ or Mn2+ and a thiol for activity. In Escherichia coli, Lys-193, Lys-194, Cys-195, His-197, and His-356 are thought to be catalytic residues, while His-184 is thought to be involved in the assembly of the tetrameric enzyme.
Between prokaryotes and eukaryotes, a difference in ICL structure is the addition of approximately 100 amino acids near the center of the eukaryotic enzyme. In eukaryotes, the additional amino acids are thought to function in the localization of ICL to single-membrane-bound organelles called glyoxysomes. These additional amino acids account for the difference in molecular mass: the prokaryotic ICL is 48kDa, while the eukaryotic ICL is 67 kDa. Only one cysteine residue is conserved between the sequences of the fungal, plant and bacterial enzymes; it is located in the middle of a conserved hexapeptide.
Read more about this topic: Isocitrate Lyase
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