Fig. 1: FAB cycle and known AcpP–PP complexes.

a A schematic representation of the chemical transformations that occur during fatty acid biosynthesis, highlighting the importance of protein–protein interactions required at each step for substrate processing. The four quadrants at the center of the scheme show the structures of all FAS AcpP crosslinked complexes solved thus far. The top two structures are the crosslinked AcpP–KSs (AcpP–FabF and AcpP–FabB) reported herein, while depicted below are the crosslinked AcpP–DHs (AcpP–FabZ and AcpP–FabA) solved and reported in previous publications^14,33. Each domain is abbreviated as follows: MAT malonyl-ACP transacylase, KS ketosynthase, KR ketoreductase, DH dehydratase, ER enoylreductase, and AT acyl transferase. AcpP-DH structures depicted in bottom two quadrants are AcpP–FabZ (PDB: 6N3P), AcpP–FabA (PDB: 4KEH). b, c Cartoon representations of the crosslinked AcpP–FabB and AcpP–FabF dimers. AcpP is colored cyan; the first KS monomer of AcpP–FabB and AcpP-FabF is colored orange or light orange, respectively, while the second is colored white in both structures. d Electrostatic potentials (ESP) maps of the FabB and AcpP monomers. e ESP maps of the FabF and AcpP monomers. In all cases, the ESP is mapped onto the Connelly surfaces of the FabF and AcpP monomers using a blue to white to red color range, spanning from +15.0 kT·e^–1 to –15.0 kT·e^–1.