Sandbox Reserved 1074

Crystal structures of InhA reveal a <scene name='69/694241/Homotetramer_subunits_labeled/1'>homotetramer</scene> (each subunit featured with a different color) in aqueous solution with separate ligand binding sites in each subunit. Each <scene name='69/694241/Monomer_subunit_no_ligands/1'>monomer</scene> subunit is composed of 289 residues and features a typical [http://en.wikipedia.org/wiki/Rossmann_fold] containing a single NADH binding site. The <scene name='69/694241/Secondary_structure_black/1'>secondary structure</scene> of InhA is made up of several alpha helices (pink), beta sheets (gold), and beta turns (white). This enzyme also features a fatty acyl binding crevice that accommodates the long-chain fatty acyl substrate (2TK) needed to synthesize mycolic acid precursors. The <scene name='69/694241/Helix6_helix7_updated/1'>alpha-6 and alpha-7 helices</scene> of the InhA form one side of the fatty acyl binding crevice, referred to as the <scene name='69/694241/Monomer_subunit_196_219/1'> substrate binding loop</scene> (residues 196-219). [[Image:Fatty Acyl Binding Crevice.jpg|thumb|200px|left|Fatty Acyl Binding Crevice (substrate binding loop in purple; substrates pictured inside the crevice)]] One side of this crevice is open and exposed to solvent, which allows the substrates to access the binding pocket of this enzyme. The size of the substrate binding loop is a primary determinant of the ability of InhA to distinguish between shorter and longer substrates and provide specificity for the enoyl-ACP reductase reaction.