QueE

queE is a bacterial gene that encodes a radical S-adenosylmethionine (SAM) enzyme involved in the biosynthesis of queuosine, a hypermodified nucleoside found in the wobble position of certain tRNAs. The QueE protein catalyzes a key rearrangement step: the conversion of 6-carboxy-5,6,7,8-tetrahydropterin (CPH4) into 7-carboxy-7-deazaguanine (CDG), a precursor on the pathway from GTP to queuosine.

Functionally, QueE is a member of the radical SAM enzyme family and contains the characteristic Cys motif that coordinates a [4Fe-4S] cluster. The enzyme uses SAM to generate a 5'-deoxyadenosyl radical that initiates a complex ring contraction and rearrangement of the pterin substrate. The product CDG is further processed by QueC, QueD, QueF and other pathway enzymes to give preQ1 and ultimately queuosine, which is incorporated into tRNA by tRNA-guanine transglycosylase.

queE is commonly found in bacteria and some archaeal genomes and is frequently located within operons or gene clusters encoding other queuosine biosynthesis proteins. Structural and biochemical studies have characterized its active site architecture and radical-based mechanism. QueE and the queuosine pathway are of interest because queuosine modification affects translational accuracy and cellular responses to environmental stresses; the distribution and regulation of the pathway vary among organisms.