Fig. 2: The proposed biosynthetic pathway of ARTs based on the two-polyketide-chain assembly model.
From: Initiating polyketide biosynthesis by on-line methyl esterification
The inset depicts the process that methyl groups are appended to C-5 and C-7 of the ACP-bound intermediates by β-branching system. The methyl group at C-5 is first installed on the β-carbonyl of nascent polyketide chain tethered on ACP (dark blue) in module 3, subsequently, C-7 methylation was formed on the intermediate tethered on module 4 ACP (orange) in a same manner. The absence of methyl groups at C-2, C-14, and C-18 were highlighted with points in green, blue, and purple corresponding to the inactivated domains Art11MT, Art13MT, and Art14MT, respectively. ACP acyl carrier protein, KS ketosynthase, KS0 non-elongating ketosynthase, KR ketoreductase, DH dehydratase, ER enoylreductase, MT methyltransferase, HMGS hydroxymethylglutaryl synthase.
