Involved in the biosynthesis of mycolic acids (PubMed:19436070, PubMed:23770708, PubMed:25467124). Forms, with FadD32, the initiation module of the mycolic condensation system (PubMed:19436070, PubMed:19477415, PubMed:25467124). Synthesizes, in coupled reaction with FadD32, the biosynthetic precursors of mycolic acids, alpha-alkyl beta-ketoacids, via the condensation of two long chain fatty acid derivatives, a very long meromycoloyl-AMP and a shorter 2-carboxyacyl-CoA (PubMed:19436070, PubMed:25467124). The acyl chain of the acyl-AMP produced by FadD32 is specifically transferred onto the N-terminal ACP domain of Pks13, and then transferred onto the KS domain. The extender unit carboxyacyl-CoA is specifically loaded onto the AT domain, which catalyzes the covalent attachment of the carboxyacyl chain to its active site, and its subsequent transfer onto the P-pant arm of the C-terminal ACP domain. The KS domain catalyzes the condensation between the two loaded fatty acyl chains to produce an alpha-alkyl beta-ketothioester linked to the C-ACP domain (PubMed:19436070). Then, the thioesterase-like domain acts as a transacylase and is responsible for both the release and the transfer of the alpha-alkyl beta-ketoacyl chain onto a polyol acceptor molecule, particularly trehalose, leading to the formation of the trehalose monomycolate precursor (PubMed:25467124). The presence of FadD32 is necessary for the transfer of the acyl chain from the AMP carrier onto Pks13. Lipid metabolism; mycolic acid biosynthesis. Made of a minimal module holding ketosynthase (KS), acyltransferase (AT), and C-terminal acyl carrier protein (C-ACP) domains, and additional N-terminal ACP (N-ACP) and C-terminal thioesterase-like domains. 4'-phosphopantetheine is transferred from CoA to specific serines of apo-Pks13 by PptT. Identified as a drug target (PubMed:23770708, PubMed:28669536, PubMed:29328655, PubMed:30875203). Fatty acyl-AMP loading is inhibited by thiophene (TP) compounds, which kill Mycobacterium tuberculosis. Overexpression of wild-type Pks13 results in TP resistance, and overexpression of the F79S mutant confers high resistance (PubMed:23770708). Structure-guided methods identified a highly potent and very safe lead compound, TAM16, a benzofuran class inhibitor that targets the thioesterase activity (PubMed:28669536). The thioesterase-like domain is inhibited by coumestan derivatives that possess excellent anti-tuberculosis activity against both the drug-susceptible and drug-resistant Mtb strains (PubMed:29328655, PubMed:30875203).