The Alkylquinolone Repertoire of Pseudomonas aeruginosa is Linked to Structural Flexibility of the FabH‐like 2‐Heptyl‐3‐hydroxy‐4(1H)‐quinolone (PQS) Biosynthesis Enzyme PqsBC

Abstract

Pseudomonas aeruginosa is a bacterial pathogen that causes life-threatening infections in immunocompromised patients. It produces a large armory of saturated and mono-unsaturated 2-alkyl-4(1H)-quinolones (AQs) and AQ N-oxides (AQNOs) that serve as signaling molecules to control the production of virulence factors and that are involved in membrane vesicle formation and iron chelation; furthermore, they also have, for example, antibiotic properties. It has been shown that the β-ketoacyl-acyl-carrier protein synthase III (FabH)-like heterodimeric enzyme PqsBC catalyzes the last step in the biosynthesis of the most abundant AQ congener, 2-heptyl-4(1H)-quinolone (HHQ), by condensing octanoyl-coenzyme A (CoA) with 2-aminobenzoylacetate (2-ABA), but the basis for the large number of other AQs/AQNOs produced by P. aeruginosa is not known. Here, we demonstrate that PqsBC uses different medium-chain acyl-CoAs to produce various saturated AQs/AQNOs and that it also biosynthesizes mono-unsaturated congeners. Further, we determined the structures of PqsBC in four different crystal forms at 1.5 to 2.7 Å resolution. Together with a previous report, the data reveal that PqsBC adopts open, intermediate, and closed conformations that alter the shape of the acyl-binding cavity and explain the promiscuity of PqsBC. The different conformations also allow us to propose a model for structural transitions that accompany the catalytic cycle of PqsBC that might have broader implications for other FabH-enzymes, for which such structural transitions have been postulated but have never been observed.

The Peptide Chain Release Factor Methyltransferase PrmC Influences the Pseudomonas aeruginosa PA14 Endo- and Exometabolome

“…The levels of the short or especially long alkyl chain AQs appeared to be more strongly affected by prmC deficiency, whereas the effect on the medium chain lengths (C6 – C9) was less pronounced. This is in accordance with recent findings on the substrate specificity of the biosynthetic enzyme complex PqsBC, which prefers medium chain activated fatty acids over long and short chain ones [ 19 ]. Krueger et al demonstrated lower levels of PqsB and PqsC in tn prmC [ 9 ].…”

Bromination of alkyl quinolones by Microbulbifer sp. HZ11, a marine Gammaproteobacterium, modulates their antibacterial activity

“…AQ synthesis is initiated by the coenzyme A ligase PqsA which activates anthranilic acid for the PqsD‐catalysed condensation with malonyl‐CoA to form 3‐(2‐aminophenyl)‐3‐oxopropanoyl‐CoA (2‐ABA‐CoA) Thioester hydrolysis by PqsE (which also can be mediated by unspecific thioesterases) leads to formation of 3‐(2‐aminophenyl)‐3‐oxopropanoic acid (2‐ABA), which in the next step is condensed with a fatty acid acyl‐CoA by PqsBC, leading to the 2‐alkyl‐1( H )‐quinolin‐4‐one. PqsBC has a preference for octanoyl‐CoA, leading to HHQ, but also utilizes longer and shorter acyl‐CoAs (Witzgall et al ., ). The monooxygenase PqsH hydroxylates 2‐alkyl‐1( H )‐quinolin‐4‐ones at C3, yielding PQS or derivatives (Fig.…”

Targeting the Pseudomonas quinolone signal quorum sensing system for the discovery of novel anti-infective pathoblockers

“…The quinolone core is formed by action of the heterodimeric complex PqsBC. This time, CoA-activated octanoic acid is used to preload an active-site cysteine of PqsC with the fatty acid via a thioester linkage [ 30 – 31 ]. The previously produced 2-ABA is then consumed to from HHQ under decarboxylative condensation [ 30 ].…”

“…This time, CoA-activated octanoic acid is used to preload an active-site cysteine of PqsC with the fatty acid via a thioester linkage [ 30 – 31 ]. The previously produced 2-ABA is then consumed to from HHQ under decarboxylative condensation [ 30 ]. Finally, PQS is produced through hydroxylation of position 3 by the NADH-dependent flavin mono-oxygenase PqsH [ 32 ].…”

“…This biosynthetic cascade is also responsible for the generation of the pqs-related metabolites DHQ, 2-AA, and HQNO as well as other AQs having different lengths of the alkyl chain [ 29 – 30 ]. Aforementioned enzyme PqsL is needed for the production of HQNO, as it delivers the N -oxidised substrate 2-HABA for PqsBC-mediated condensation with octanoyl-CoA analogous to HHQ biosynthesis [ 27 ].…”