2-isopropylmalate synthase

2-isopropylmalate synthase
Identifiers
EC number	2.3.3.13
CAS number	9030-98-2
Databases
IntEnz	IntEnz view
BRENDA	BRENDA entry
ExPASy	NiceZyme view
KEGG	KEGG entry
MetaCyc	metabolic pathway
PRIAM	profile
PDB structures	RCSB PDB PDBe PDBsum
Gene Ontology	AmiGO / EGO
Search PMC articles PubMed articles NCBI proteins

In enzymology, a 2-isopropylmalate synthase (EC 2.3.3.13) is an enzyme that catalyzes the chemical reaction

acetyl-CoA + 3-methyl-2-oxobutanoate + H₂O $\rightleftharpoons$ (2S)-2-isopropylmalate + CoA

The three substrates of this enzyme are acetyl-CoA, 3-methyl-2-oxobutanoate, and H₂O, and its products are (2S)-2-isopropylmalate and CoA.

The enzyme belongs to the family of transferases, specifically those acyltransferases that convert acyl groups into alkyl groups on transfer. The systematic name of this enzyme class is acetyl-CoA:3-methyl-2-oxobutanoate C-acetyltransferase (thioester-hydrolysing, carboxymethyl-forming). Other names in common use include 3-carboxy-3-hydroxy-4-methylpentanoate 3-methyl-2-oxobutanoate-lyase, (CoA-acetylating), alpha-isopropylmalate synthetase, alpha-isopropylmalate synthase, alpha-isopropylmalic synthetase, isopropylmalate synthase, and isopropylmalate synthetase. This enzyme participates in biosynthesis of L-leucine and pyruvate metabolism. Monovalent and divalent cation activation have been reported for enzymes from different sources.^[1][2][3]

Mycobacterium tuberculosis α-isopropylmalate synthase requires a divalent metal ion, of which Mg²⁺ and Mn²⁺ give highest activity, and a monovalent cation, with K⁺ as the best activator.^[4][5] Zn²⁺ was shown to be an inhibitor, contrary to what was assumed from the structural data. In addition to the complex requirements for a divalent metal and further activation by K⁺, M. tuberculosis α-isopropylmalate synthase follows a random kinetic mechanism for catalysis. Another feature of the M. tuberculosis homolog is that L-leucine, the feedback inhibitor, inhibits the enzyme in a time-dependent fashion. This was the first demonstration of a feedback inhibitor that displays slow-onset inhibition.^[6]

Structural studies

As of late 2007, only one structure has been solved for this class of enzymes, with the PDB accession code 1SR9.

References

1. Cole FE, Kalyanpur MG, Stevens CM (1973). "Absolute configuration of alpha isopropylmalate and the mechanism of its conversion to beta isopropylmalate in the biosynthesis of leucine". Biochemistry. 12 (17): 3346–50. doi:10.1021/bi00741a031. PMID 4270046.
2. Kohlhaw G, Leary TR, Umbarger HE (1969). "Alpha-isopropylmalate synthase from Salmonella typhimurium Purification and properties". J. Biol. Chem. 244 (8): 2218–25. PMID 4976555.
3. Webster RE and Gross, SR (1965). "The alpha-isopropylmalate synthetase of Neurospora. I. The kinetics and end product control of alpha-isopropylmalate synthetase function". Biochemistry 4 (11): 2309–2327. doi:10.1021/bi00887a008.
4. Carvalho LP, Blanchard, JS (2006). "Kinetic and Chemical Mechanism of alpha-Isopropylmalate Synthase from Mycobacterium tuberculosis". Biochemistry. 45 (29): 8988–99. doi:10.1021/bi0606602. PMC 2507874. PMID 16846242.
5. Carvalho LP, Blanchard, JS (2006). "Kinetic analysis of the effects of monovalent cations and divalent metals on the activity of Mycobacterium tuberculosis alpha-isopropylmalate synthase". Archives of Biochemistry and Biophysics 451 (2): 141–48. doi:10.1016/j.abb.2006.03.030. PMID 16684501.
6. Carvalho LP, Argyrou A, Blanchard, JS (2005). "Slow-onset Feedback Inhibition: Inhibition of Mycobacterium tuberculosis alpha-Isopropylmalate Synthase by L-Leucine". Journal of the American Chemical Society 127 (28): 10004–5. doi:10.1021/ja052513h. PMID 16011356.