Download citation
Download citation
link to html
Ketosynthases (KSs) catalyse essential carbon–carbon bond-forming reactions in fatty-acid biosynthesis using a two-step, ping-pong reaction mechanism. In Escherichia coli, there are two homodimeric elongating KSs, FabB and FabF, which possess overlapping substrate selectivity. However, FabB is essential for the biosynthesis of the unsaturated fatty acids (UFAs) required for cell survival in the absence of exogenous UFAs. Additionally, FabB has reduced activity towards substrates longer than 12 C atoms, whereas FabF efficiently catalyses the elongation of saturated C14 and unsaturated C16:1 acyl-acyl carrier protein (ACP) complexes. In this study, two cross-linked crystal structures of FabB in complex with ACPs functionalized with long-chain fatty-acid cross-linking probes that approximate catalytic steps were solved. Both homodimeric structures possess asymmetric substrate-binding pockets suggestive of cooperative relationships between the two FabB monomers when engaged with C14 and C16 acyl chains. In addition, these structures capture an unusual rotamer of the active-site gating residue, Phe392, which is potentially representative of the catalytic state prior to substrate release. These structures demonstrate the utility of mechanism-based cross-linking methods to capture and elucidate conformational transitions accompanying KS-mediated catalysis at near-atomic resolution.

Supporting information

pdf

Portable Document Format (PDF) file https://doi.org/10.1107/S2059798322007434/jb5047sup1.pdf
Supplementary Figures and synthesis of cross-linking probes.

mp4

Moving Picture Experts Group (MP4) video file https://doi.org/10.1107/S2059798322007434/jb5047sup2.mp4
Supplementary Movie S1.

PDB references: FabB cross-linked with C14-ACP, 7sqi; FabB cross-linked with C16:1-ACP, 7sz9


Follow Acta Cryst. D
Sign up for e-alerts
Follow Acta Cryst. on Twitter
Follow us on facebook
Sign up for RSS feeds