期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2015
卷号：112
期号：41
页码：12693-12698
DOI：10.1073/pnas.1515460112
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceThere are many differences in the sequences of ketosynthase (KS) domains from the well-studied type I polyketide synthases (PKSs) and the more recently discovered acyltransferase (AT)-less type I PKSs. The AT-less type I PKSs generate polyketides with a high degree of structural diversity, which stems from their evolution by horizontal gene transfer. In comparison, canonical type I PKSs evolve by gene duplication. The seven structures of AT-less type I PKS KSs reveal the molecular details surrounding the evolution of substrate specificity and structural diversity, and their overall differences with canonical type I PKS KSs. Understanding the mechanism of substrate specificity will allow reprogramming of the KS active sites to generate polyketide analogues by PKS and polyketide biosynthetic pathway engineering. Acyltransferase (AT)-less type I polyketide synthases (PKSs) break the type I PKS paradigm. They lack the integrated AT domains within their modules and instead use a discrete AT that acts in trans, whereas a type I PKS module minimally contains AT, acyl carrier protein (ACP), and ketosynthase (KS) domains. Structures of canonical type I PKS KS-AT didomains reveal structured linkers that connect the two domains. AT-less type I PKS KSs have remnants of these linkers, which have been hypothesized to be AT docking domains. Natural products produced by AT-less type I PKSs are very complex because of an increased representation of unique modifying domains. AT-less type I PKS KSs possess substrate specificity and fall into phylogenetic clades that correlate with their substrates, whereas canonical type I PKS KSs are monophyletic. We have solved crystal structures of seven AT-less type I PKS KS domains that represent various sequence clusters, revealing insight into the large structural and subtle amino acid residue differences that lead to unique active site topologies and substrate specificities. One set of structures represents a larger group of KS domains from both canonical and AT-less type I PKSs that accept amino acid-containing substrates. One structure has a partial AT-domain, revealing the structural consequences of a type I PKS KS evolving into an AT-less type I PKS KS. These structures highlight the structural diversity within the AT-less type I PKS KS family, and most important, provide a unique opportunity to study the molecular evolution of substrate specificity within the type I PKSs.
