The LINKS motif zippers trans-acyltransferase polyketide synthase assembly lines into a biosynthetic megacomplex

Abstract

Polyketides such as the clinically-valuable antibacterial agent mupirocin are constructed by architecturally-sophisticated assembly lines known as trans-acyltransferase polyketide synthases. Organelle-sized megacomplexes composed of several copies of trans-acyltransferase polyketide synthase assembly lines have been observed by others through transmission electron microscopy to be located at the Bacillus subtilis plasma membrane, where the synthesis and export of the antibacterial polyketide bacillaene takes place. In this work we analyze ten crystal structures of trans-acyltransferase polyketide synthases ketosynthase domains, seven of which are reported here for the first time, to characterize a motif capable of zippering assembly lines into a megacomplex. While each of the three-helix LINKS (Laterally-INteracting Ketosynthase Sequence) motifs is observed to similarly dock with a spatially-reversed copy of itself through hydrophobic and ionic interactions, the amino acid sequences of this motif are not conserved. Such a code is appropriate for mediating homotypic contacts between assembly lines to ensure the ordered self-assembly of a noncovalent, yet tightly-knit, enzymatic network. LINKS-mediated lateral interactions would also have the effect of bolstering the vertical association of the polypeptides that comprise a polyketide synthase assembly line.

Portability and Structure of the Four-Helix Bundle Docking Domains of trans-Acyltransferase Modular Polyketide Synthases

“…4,5 While protein–protein interactions are known to mediate the ordered assembly of PKS polypeptides, how they do so remains a subject of active investigation. 6,7 …”

Acyltransferases as Tools for Polyketide Synthase Engineering

“…A different approach to the whole domain swapping, aiming at the substitution of AT-substrate specificity, is the site-directed mutagenesis ( Figure 5 ). Recent advances in sequencing methodology, bioinformatics, structural and synthetic biology contributed to the identification of amino acid signatures of ATs and have a significant impact on the engineering of PKS assembly lines [ 49 , 61 , 74 , 106 , 113 , 138 , 143 , 144 , 148 , 156 , 157 , 158 , 159 , 160 , 161 , 162 , 163 , 164 , 165 , 166 , 167 , 168 , 169 ].…”

On‐Line Polyketide Cyclization into Diverse Medium‐Sized Lactones by a Specialized Ketosynthase Domain

“…Excluding the conserved catalytic residues, ten positions in the family of branching KSs differ considerably when compared with classical KSs mediating Claisen condensations (see Table S1 and Figure S1 in the Supporting Information). Conserved residues of the Rhi‐KS14 (PDB code: 4kc5) were mapped and superimposed on the bacillaene KS5 structure (PDB code: 5erb, Figure A) . These residues were mutated to the corresponding residues represented in the canonical KSs.…”