The Mycobacterium tuberculosis very-long-chain fatty acyl-CoA synthetase: structural basis for housing lipid substrates longer than the enzyme.

The Mycobacterium tuberculosis acid-induced operon MymA encodes the fatty acyl-CoA synthetase FadD13 and is essential for virulence and intracellular growth of the pathogen. Fatty acyl-CoA synthetases activate lipids before entering into the metabolic pathways and are also involved in transmembrane lipid transport. Unlike soluble fatty acyl-CoA synthetases, but like the mammalian integral-membrane very-long-chain acyl-CoA synthetases, FadD13 accepts lipid substrates up to the maximum length tested (C(26)). Here, we show that FadD13 is a peripheral membrane protein. The structure and mutational studies reveal an arginine- and aromatic-rich surface patch as the site for membrane interaction. The protein accommodates a hydrophobic tunnel that extends from the active site toward the positive patch and is sealed by an arginine-rich lid-loop at the protein surface. Based on this and previous data, we propose a structural basis for accommodation of lipid substrates longer than the enzyme and transmembrane lipid transport by vectorial CoA-esterification.