PMID: 23163771

Authors:

Dutta D, Bhattacharyya S, Roychowdhury A, Biswas R, Das AK

Title:

Crystal structure of Hexanoyl-CoA bound to beta-ketoacyl reductase FabG4 of Mycobacterium tuberculosis.

Journal:

Biochem J. 2012 Nov 19.

Abstract:

FabGs or beta-ketoacyl reductases are involved in fatty acid synthesis. The reaction entails NADPH/NADH mediated conversion of beta-ketoacyl-ACP to beta-hydroxyacyl-ACP. High molecular weight FabGs (HMwFabG) form a phylogenetically separate group of FabG enzymes. FabG4, an HMwFabG of Mycobacterium tuberculosis, comprises of two distinct domains Nterminal "flavodoxin type" domain and C-terminal ketoreductase domain. The catalytically active C-terminal domain utilizes NADH to reduce beta-ketoacyl-CoA to beta-hydroxyacyl-CoA. Here the crystal structures of FabG4:NADH binary complex and FabG4:NAD+:HexanoylCoA ternary complex have been determined to understand its substrate specificity and catalytic mechanism. This is the first report to demonstrate how FabG4 interacts with its coenzyme NADH and hexanoyl-CoA that mimics an elongating fattyacyl chain covalently linked with coenzyme A. Structural analysis shows that the binding of hexanoyl-CoA within the active site cavity of FabG significantly differs from that of the C16-fattyacyl substrate bound to Mycobacterial FabI (InhA). The ternary complex reveals that both loop-I and loop-II interacts with the phosphopantetheine moiety of CoA or ACP to align the covalently linked fattyacyl substrate near the active site. Structural evidences and ACP inhibition studies indicates that FabG4 can accepts both CoA and ACP based fattyacyl substrates. We have also shown that in FabG4-dimer Arg146 and Arg445 of one monomer interact with the C-terminus of the second monomer to play pivotal role in substrate association and catalysis.