Mechanism of the Quorum-Quenching Lactonase (AiiA) from Bacillus thuringiensis. 1. Product-Bound Structures

Abstract

Enzymes capable of hydrolyzing N-acyl-l-homoserine lactones (AHLs) used in some bacterial quorum-sensing pathways are of considerable interest for their ability to block undesirable phenotypes. Most known AHL hydrolases that catalyze ring opening (AHL lactonases) are members of the metallo-β-lactamase enzyme superfamily and rely on a dinuclear zinc site for catalysis and stability. Here we report the three-dimensional structures of three product complexes formed with the AHL lactonase from Bacillus thuringiensis. Structures of the lactonase bound with two different concentrations of the ring-opened product of N-hexanoyl-l-homoserine lactone are determined at 0.95 and 1.4 Å resolution and exhibit different product configurations. A structure of the ring-opened product of the non-natural N-hexanoyl-l-homocysteine thiolactone at 1.3 Å resolution is also determined. On the basis of these product-bound structures, a substrate-binding model is presented that differs from previous proposals. Additionally, the proximity of the product to active-site residues and observed changes in protein conformation and metal coordination provide insight into the catalytic mechanism of this quorum-quenching metalloenzyme.

Exploiting Quorum Sensing To Confuse Bacterial Pathogens

“…Hydrolysis of this ester bond can also occur spontaneously at alkaline pH, and acidic conditions can restore the bond and AHL signaling activity following biological or abiotic hydrolysis (86). Lactonases generally have very broad AHL substrate specificity, likely due to the fact that the targeted homoserine lactone ring is conserved among all AHLs and the variable acyl chain makes only nonspecific interac-tions within the active-site cavity of the enzyme (58). In contrast, AHL acylases hydrolyze the acyl-amide bond between the acyl tail and latone ring of AHLs in a nonreversible manner, resulting in the release of a fatty acid chain and a homoserine lactone moiety ( Fig.…”

Dynamics in the mixed microbial concourse

“…Negative feedback was integrated with a basic QS system with the help of another new component from nature. The AiiA enzyme from Bacillus thurigiensis degrades AHL compounds by hydrolyzing the homoserine ring (Liu et al 2008). The degradation product is no longer able to activate a QS response.…”

The quorum-quenching N -acyl homoserine lactone acylase PvdQ is an Ntn-hydrolase with an unusual substrate-binding pocket

“…This enzyme disrupts quorum sensing by cleaving the ester bond in the homoserine lactone ring, making it inactive in signaling. The lactonase structures show that the AHL acyl chain binds in a solvent-exposed groove along the enzyme surface, allowing the binding of acyl chains of different lengths (11). Huang et al (12) and Sio et al (13) have characterized a different quorumquenching enzyme from the opportunistic pathogen Pseudomonas aeruginosa, which prefers long-chain AHLs such as C 10 to C 14 .…”