Involved in the biosynthesis of phthiocerol dimycocerosate (PDIM), a cell wall-associated lipid found only in pathogenic mycobacteria. 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. 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] Lipid metabolism; fatty acid biosynthesis. Disruption mutant lacks the ability to produce mycosides and mycocerosyl phthiocerol esters. Belongs to the ATP-dependent AMP-binding enzyme family.