Dual role of isocitrate lyase 1 in the glyoxylate and methylcitrate cycles in Mycobacterium tuberculosis.
The role of isocitrate lyase (ICL) in the glyoxylate cycle and its necessity for persistence and virulence of Mycobacterium tuberculosis has been well described. Recent reports have alluded to an additional role for this enzyme in M. tuberculosis metabolism, specifically for growth on propionate. A product of beta-oxidation of odd-chain fatty acids is propionyl-CoA. Clearance of propionyl-CoA and the by-products of its metabolism via the methylcitrate cycle is vital due to their potentially toxic effects. Although the genome of M. tuberculosis encodes orthologues of two of the three enzymes of the methylcitrate cycle, methylcitrate synthase and methylcitrate dehydratase, it does not appear to contain a distinct 2-methylisocitrate lyase (MCL). Detailed structural analysis of the MCL from Escherichia coli suggested that the differences in substrate specificity between MCLs and ICLs could be attributed to three conserved amino acid substitutions in the active site, suggesting an MCL signature. However, here we provide enzymatic evidence that shows that despite the absence of the MCL signature, ICL1 from M. tuberculosis can clearly function as a MCL. Furthermore, the crystal structure of ICL1 with pyruvate and succinate bound demonstrates that the active site can accommodate the additional methyl group without significant changes to the structure.
Gould
Ty A
TA
Department of Biochemistry and Biophysics, Texas A & M University, College Station, TX 77843, USA.
van de Langemheen
Helmus
H
Muñoz-Elías
Ernesto J
EJ
McKinney
John D
JD
Sacchettini
James C
JC
D001426:Bacterial Proteins / Q000737:chemistry* / Q000302:isolation & purification; D019755:Carbon-Carbon Lyases / Q000378:metabolism; D002950:Citrate (si)-Synthase / Q000378:metabolism; D002951:Citrates / Q000378:metabolism*; D003461:Crystallography; D005227:Fatty Acids / Q000378:metabolism; D006038:Glyoxylates / Q000378:metabolism*; D007522:Isocitrate Lyase / Q000737:chemistry* / Q000302:isolation & purification; D008958:Models, Molecular; D009169:Mycobacterium tuberculosis / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D011487:Protein Conformation; D019289:Pyruvic Acid / Q000378:metabolism; D019802:Succinic Acid / Q000378:metabolism
D001426:Bacterial Proteins; D002951:Citrates; D005227:Fatty Acids; D006038:Glyoxylates; D019289:Pyruvic Acid; D019802:Succinic Acid; D002950:Citrate (si)-Synthase; D019755:Carbon-Carbon Lyases; C402427:icl protein, Mycobacterium; C092884:methylcitrate synthase; D007522:Isocitrate Lyase; C417277:methylisocitrate lyase; C031150:glyoxylic acid