Fig. S1

Biogenesis of Q derivatives and reaction mechanisms of Q-glycosylations, related to Figures 1, 3, and 6 (A) Chemical structures with atom numbering of Q (left), galQ (middle), and manQ (right). (B) Queuosine biosynthesis in bacteria. A queuosine (Q) precursor base, 7-cyano-7-deazaguanine (preQ1), is generated from GTP through five step reaction; preQ1 is then inserted at the first position of the tRNA anticodon via a base-exchanging reaction catalyzed by tRNA guanine transglycosylase (TGT), followed by two steps to complete Q biogenesis on tRNA. Q or queuine (q) originating from Q-tRNA degradation or the diet is incorporated into animal cells. The DUF2419 protein (C9orf64 in human) is believed to release q from Q in the cytoplasm of animal cells. The QTRT1/QTRT2 heterodimer, a eukaryotic TGT, inserts q into cytoplasmic tRNAs for Tyr, Asp, His, and Asn. QTGAL galactosylates Q34 using UDP-gal to form galQ34 of tRNATyr. QTMAN mannosylates Q34 using GDP-man to form manQ34 of tRNAAsp. The QTRT1/QTRT2 heterodimer is also responsible for Q34 formation in mitochondrial tRNAs for Tyr, Asp, His, and Asn. 7-deazaguanosine derivatives are colored blue. GTP, guanosine triphosphate; DH2NTP, 7,8-dihydroneopterine triphosphate; CPH4, 6-carboxy-5,6,7,8-tetrahydropterin; CDG, 7-carboxy-7-deazaguanine; preQ0, 7-cyano-7-deazaguanine; oQ, epoxyqueuosine; Gua, guanosine. (C) Classification of Q-glycosylation as inverting or retaining based on the anomeric configuration of the sugar donor in the products. (D) Possible mechanism of the SN2 inverting reaction catalyzed by QTGAL. The amino acid residue numbers are from human QTGAL. (E) Possible mechanism of the SNi-like retaining reaction catalyzed by QTMAN. The amino acid residue numbers are from human QTMAN.