Involved in the biosynthesis of phthiocerol dimycocerosate (PDIM), a cell wall-associated lipid found only in pathogenic mycobacteria (PubMed:10573420, PubMed:11279114). Catalyzes the activation of long-chain fatty acids as acyl-adenylates (acyl-AMP), which are then transferred to the multifunctional polyketide synthase Mas for further chain extension (PubMed:24831705). Probably plays a role in host phagosome maturation arrest (Probable). a long-chain fatty acid + ATP + holo-[mycocerosate synthase] = AMP + diphosphate + long-chain fatty acyl-[mycocerosate synthase] a long-chain fatty acid + ATP + H(+) = a long-chain fatty acyl-AMP + diphosphate a long-chain fatty acyl-AMP + holo-[mycocerosate synthase] = AMP + H(+) + long-chain fatty acyl-[mycocerosate synthase] ATP + dodecanoate + H(+) = diphosphate + dodecanoyl-AMP ATP + H(+) + hexadecanoate = diphosphate + hexadecanoyl-AMP Inhibited by acylsulfamoyl (acyl-AMS) analogs. Lipid metabolism; fatty acid biosynthesis. Disruption of fadD28 abolishes the production of phthiocerol dimycocerosate (DIM) on the cell envelope (PubMed:10573420, PubMed:11279114). Grows normally in liquid culture, traffics into host (human and mouse) acidified compartments early after phagocytosis, suggesting it no longer arrests phagosome maturation as well as wild-type, impaired growth in mouse macrophages (PubMed:20844580). Belongs to the ATP-dependent AMP-binding enzyme family.