Sandbox Reserved 1058: Difference between revisions

[[Image:Active Site Residues.png|250 px|left|thumb|'''Figure 3. Active Site Residues.''' All eight active site residues necessary for catalysis of isocitrate are shown in slate. However, the protein shown is a C191S mutant of isocitrate lyase.]] [[Image:Active_Site_Hydrogen_Bonding.png|250 px|right|thumb|'''Figure 4. Active site residues hydrogen bound to a cofactor and the products of the catalyzed isocitrate reaction.''' Glyoxylate is shown in blue, succinate is shown in green, and the Mg²⁺ cofactor is shown in yellow.]] The active site of isocitrate lyase consists of eight residues: Trp93, Cys191, His193, Ser315, Ser317, Asn313, Thr347, Leu348 (Figure 3). Additionally, there are several other amino acid side chains present that form hydrogen bonding opportunities with isocitrate to catalyze the breakdown reaction to glyoxylate and succinate. Ser91, Gly92, Trp93, and Arg228 form hydrogen bonds with glyoxylate while Asn313, Glu295, Arg228, and Gly192 and Trp93, Thr347, Ser315, Ser317, and His193 form hydrogen bonding opportunities with the two carboxylates within succinate. <ref name="sharma"> Sharma, V.; Sharma, S.; Hoener zu Bentrup, K.; McKinney, J.; Russell, D.; ''et. al''; Structure of isocitrate lyase, a persistence factor of ''Mycobacterium tuberculosis''. ''Nat. Struct. Biol.''. '''2000'''. ''7(8)'':663-668. </ref> Additionally, a Mg²⁺ ion is needed for further electrostatic stabilization of the extreme negative charge on isocitrate. This Mg²⁺ hydrogen bonds to the carboxylate in glyoxylate and one of the carboxylates in succinate.