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Queuosine (Q) is a modification of the wobble base of tRNA harboring GUN antico-dons with roles in decoding accuracy and efficiency. Its synthesis is complex with mul-tiple enzymatic steps and several pathway intermediates can be salvaged. The only two transporter families known to salvage Q precursors are QPTR/COG1738 and QrtT/QueT. Analysis of the distribution of known Q synthesis and salvage genes in human gut and oral microbiota genomes have suggested that more transporter fami-lies remained to be found and that Q precursor exchanges must occur within the struc-tured microenvironments of the mammalian host. Using physical clustering and fu-sion-based association with Q salvage genes, candidate genes for missing transporters were identified and five were tested experimentally by complementation assays in Escherichia coli. Three genes encoding transporters from three different Pfam families, a Ureide permease (PF07168) from Acidobacteriota bacterium, a Hemolysin III family pro-tein (PF03006) from Bifidobacterium breve, and a Major Facilitator Superfamily protein (PF07690) from Bartonella henselae, were found to allow the transport of both preQ0 and preQ1 in this heterologous system. This work suggests that many transporter families can evolve to transport Q precursors reinforcing the concept of transporter plasticity.
Quaiyum et al. (Tue,) studied this question.