Sandbox Reserved 1056: Difference between revisions

The two inhibitors used to elucidate the structure of ICL were 3-nitropropionate and 3-bromopyruvate.  The 3-nitropropionate was used to mimic the succinate, while the 3-bromopyruvate is used to mimic the glyoxylate.  These two inhibitors have also been shown to be good inhibitors of isocitrate lyase in ''M. avium'' indicating that their inhibitory capacity is conserved across multiple species.<ref name="ICL">PMID:10932251</ref> A mutant isocitrate lyase C191S, in conjunction with the aforementioned substrate mimics, was used to elucidate the first high resolution crystal structure of ICL.<ref name="ICL">PMID:10932251</ref> Dehalogenated 3-bromopyruvate works to inhibit isocitrate lyase by forming a covalent bond with the Ser191 in the active site, which can be found crystallized here [[1f8m]].  This 3-bromopyruvate occupies the same site that the succinate would occupy.  The C191S mutant adopts a conformation almost identical to the CYS191 residue in the wild type indicating that this is an accurate depiction of the conformation. <ref name="ICL">PMID:10932251</ref>   

Isocitrate lyase catalyzes a reversible aldol condensation, converting isocitrate to glyoxylate and succinate via the breaking of a C-C bond.<ref name="claisen"/> Within the active site of ICL the HIS193 residue deprotonates the <scene name='69/694223/Arginine/3'>Cys191</scene>residue of the active site in order to increase its basicity.<ref name="ICL">PMID:10932251</ref><ref name="claisen"/> The Cys 191 residue then deprotonates the alpha carbon adjacent to one of the carbonyl groups of succinate, thus forming the enolic intermediate<ref name="claisen"/>. The negatively charged alpha carbon atom of the enolic intermediate acts as a nucleophile that attacks the carbonyl carbon of the aldehyde of glyoxylate.  The nucleophilic attack will place a negative charge on the oxygen atom oxygen at the former carbonyl oxygen of the aldehyde, which will be stabilized by positive charges of the Mg ion, ARG228 and HIS180.<ref name="ICL">PMID:10932251</ref> The protonation of this species will yield the final product. It is important to note that this reaction is entirely reversible; the breakdown of isocitrate into glyoxylate and succinate occurs using a similar mechanism.