title: Acyl-ACP substrate recognition in Burkholderia mallei BmaI1 acyl-homoserine lactone synthase.
abstract: The acyl-homoserine lactone (AHL) autoinducer mediated quorum sensing regulates virulence in several pathogenic bacteria. The hallmark of an efficient quorum sensing system relies on the tight specificity in the signal generated by each bacterium. Since AHL signal specificity is derived from the acyl-chain of the acyl-ACP (ACP = acyl carrier protein) substrate, AHL synthase enzymes must recognize and react with the native acyl-ACP with high catalytic efficiency while keeping reaction rates with non-native acyl-ACPs low. The mechanism of acyl-ACP substrate recognition in these enzymes, however, remains elusive. In this study, we investigated differences in catalytic efficiencies for shorter and longer chain acyl-ACP substrates reacting with an octanoyl-homoserine lactone synthase Burkholderia mallei BmaI1. With the exception of two-carbon shorter hexanoyl-ACP, the catalytic efficiencies of butyryl-ACP, decanoyl-ACP, and octanoyl-CoA reacting with BmaI1 decreased by greater than 20-fold compared to the native octanoyl-ACP substrate. Furthermore, we also noticed kinetic cooperativity when BmaI1 reacted with non-native acyl-donor substrates. Our kinetic data suggest that non-native acyl-ACP substrates are unable to form a stable and productive BmaI1·acyl-ACP·SAM ternary complex and are thus effectively discriminated by the enzyme. These results offer insights into the molecular basis of substrate recognition for the BmaI1 enzyme.
authors.affiliation: Department of Chemistry and Biochemistry, Boise State University , 1910 University Drive, Boise, Idaho 83725, United States.
authors.forename: Aubrey N
authors.initials: AN
authors.lastname: Montebello
authors.forename: Ryan M
authors.initials: RM
authors.lastname: Brecht
authors.forename: Remington D
authors.initials: RD
authors.lastname: Turner
authors.forename: Miranda
authors.initials: M
authors.lastname: Ghali
authors.forename: Xinzhu
authors.initials: X
authors.lastname: Pu
authors.forename: Rajesh
authors.initials: R
authors.lastname: Nagarajan
mesh_terms: D000213:Acyl Carrier Protein / Q000378:metabolism*; D054742:Acyl-Butyrolactones / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D055162:Biocatalysis; D042726:Burkholderia mallei / Q000201:enzymology / Q000235:genetics / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D007700:Kinetics; D008025:Ligases / Q000235:genetics / Q000378:metabolism*; D013379:Substrate Specificity
chemical_list: D000213:Acyl Carrier Protein; D054742:Acyl-Butyrolactones; D001426:Bacterial Proteins; D008025:Ligases