High-resolution structures of AidH complexes provide insights into a novel catalytic mechanism for N-acyl homoserine lactonase

Acta Crystallogr D Biol Crystallogr. 2013 Jan;69(Pt 1):82-91. doi: 10.1107/S0907444912042369. Epub 2012 Dec 20.

Abstract

Many pathogenic bacteria that infect humans, animals and plants rely on a quorum-sensing (QS) system to produce virulence factors. N-Acyl homoserine lactones (AHLs) are the best-characterized cell-cell communication signals in QS. The concentration of AHL plays a key role in regulating the virulence-gene expression and essential biological functions of pathogenic bacteria. N-Acyl homoserine lactonases (AHL-lactonases) have important functions in decreasing pathogenicity by degrading AHLs. Here, structures of the AHL-lactonase from Ochrobactrum sp. (AidH) in complex with N-hexanoyl homoserine lactone, N-hexanoyl homoserine and N-butanoyl homoserine are reported. The high-resolution structures together with biochemical analyses reveal convincing details of AHL degradation. No metal ion is bound in the active site, which is different from other AHL-lactonases, which have a dual Lewis acid catalysis mechanism. AidH contains a substrate-binding tunnel between the core domain and the cap domain. The conformation of the tunnel entrance varies with the AHL acyl-chain length, which contributes to the binding promiscuity of AHL molecules in the active site. It also supports the biochemical result that AidH is a broad catalytic spectrum AHL-lactonase. Taken together, the present results reveal the catalytic mechanism of the metal-independent AHL-lactonase, which is a typical acid-base covalent catalysis.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Carboxylic Ester Hydrolases / chemistry*
  • Carboxylic Ester Hydrolases / genetics
  • Catalysis
  • Catalytic Domain / genetics
  • Cell Communication / genetics
  • Hydrogen-Ion Concentration
  • Hydrolysis
  • Mutagenesis, Site-Directed
  • Ochrobactrum / enzymology*
  • Ochrobactrum / pathogenicity
  • Quorum Sensing / genetics
  • Substrate Specificity / genetics

Substances

  • Carboxylic Ester Hydrolases
  • N-acyl homoserine lactonase