luxAgene fromEnhygromyxa salinaencodes a functional homodimeric luciferase

Abstract

AbstractSeveral clades of luminescent bacteria are known currently. They all contain similarluxoperons, which include the genesluxAandluxBencoding a heterodimeric luciferase. The aldehyde oxygenation reaction is catalyzed by the subunit LuxA, while LuxB is inactive. Recently, genomic analysis identified a subset of bacterial species with rearrangedluxoperons lackingluxB. Here, we show thatEscherichia colitransformed with a syntheticluxAgene from the reducedluxACDEoperon ofEnhygromyxa salinais luminescent upon addition of aldehydes. Overall,EsLuxA is less bright compared to luciferases fromAliivibrio fischeri(AfLuxAB) andPhotorhabdus luminescens(PlLuxAB), and most active with medium-chain C4-C9 aldehydes. Crystal structure ofEsLuxA determined at the resolution of 2.71 Å reveals a classical monooxygenase fold, and the protein preferentially forms a dimer in solution. The mobile loop residues 264-293, which form a β-hairpin or a coil inVibrio harveyiLuxA, form α-helices inEsLuxA. Phylogenetic analysis showsEsLuxA and related proteins may be bacterial protoluciferases that arose prior to duplication of theluxAgene and its speciation toluxAandluxBin the previously described luminescent bacteria. Our work paves the way for discovery of new luciferases that have an advantage of being encoded by a single gene.