The antigen 85 proteins (FbpA, FbpB, FbpC) are responsible for the high affinity of mycobacteria to fibronectin, a large adhesive glycoprotein, which facilitates the attachment of M.tuberculosis to murine alveolar macrophages (AMs). They also help to maintain the integrity of the cell wall by catalyzing the transfer of mycolic acids to cell wall arabinogalactan and through the synthesis of alpha,alpha-trehalose dimycolate (TDM, cord factor). They catalyze the transfer of a mycoloyl residue from one molecule of alpha,alpha-trehalose monomycolate (TMM) to another TMM, leading to the formation of TDM. a 1,2-diacyl-sn-glycerol + an acyl-CoA = a triacyl-sn-glycerol + CoA 2 alpha,alpha'-trehalose 6-mycolate = alpha,alpha'-trehalose 6,6'-bismycolate + alpha,alpha-trehalose Inhibited by 6-azido-6-deoxy-alpha,alpha-trehalose (ADT). Homodimer. Cells lacking this gene transfer 40% fewer mycolates to the cell wall with no change in the types of mycolates esterified to arabinogalactan or in the composition of non-covalently linked mycolates. As a consequence, the diffusion of hydrophobic chenodeoxycholate and of hydrophilic glycerol through the cell envelope occurs much more rapidly in mutant cells than in wild-type. Was identified as a high-confidence drug target. Belongs to the mycobacterial A85 antigen family.