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Biosynthesis of t-Butyl in apratoxin A: functional analysis and architecture of a PKS loading module

TitleBiosynthesis of t-Butyl in apratoxin A: functional analysis and architecture of a PKS loading module
Publication TypeJournal Article
Year of Publication2018
AuthorsSkiba M.A, Sikkema A.P, Moss N.A, Lowell A.N, Su M., Sturgis R.M, Gerwick L, Gerwick WH, Sherman D.H, Smith J.L
JournalAcs Chemical Biology
Date Published2018/06
Type of ArticleArticle
ISBN Number1554-8929
Accession NumberWOS:000435746200027
KeywordsBiochemistry & Molecular Biology; carrier domains; crystal-structure; cyanobacterium lyngbya-majuscula; decarboxylase; marine natural-products; mass-spectrometry; methylation; methyltransferase; polyketide; potent; synthase

The unusual feature of a t-butyl group is found in several marine-derived natural products including apratoxin A, a Sec61 inhibitor produced by the cyanobacterium Moorea bouillonii PNG 5-198. Here, we determine that the apratoxin A t-butyl group is formed as a pivaloyl acyl carrier protein (ACP) by AprA, the polyketide synthase (PKS) loading module of the apratoxin A biosynthetic pathway. AprA contains an inactive "pseudo" GCN5-related N-acetyltransferase domain (Psi GNAT) flanked by two methyltransferase domains (MT1 and MT2) that differ distinctly in sequence. Structural, biochemical, and precursor incorporation studies reveal that MT2 catalyzes unusually coupled decarboxylation and methylation reactions to transform dimethylmalonyl-ACP, the product of MT1, to pivaloyl-ACP. Further, pivaloyl-ACP synthesis is primed by the fatty acid synthase malonyl acyltransferase (FabD), which compensates for the Psi GNAT and provides the initial aryl-transfer step to form AprA malonyl-ACP. Additionally, images of AprA from negative stain electron microscopy reveal multiple conformations that may facilitate the individual catalytic steps of the multienzyme module.

Short TitleACS Chem. Biol.
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