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Adaptation of the Romanomermis culicivorax CCA-Adding Enzyme to Miniaturized Armless tRNA SubstratesHennig, Oliver, Philipp, Susanne, Bonin, Sonja, Rollet, Kévin, Kolberg, Tim, Jühling, Tina, Betat, Heike, Sauter, Claude, Mörl, Mario 10 January 2024 (has links)
The mitochondrial genome of the nematode Romanomermis culicivorax encodes for
miniaturized hairpin-like tRNA molecules that lack D- as well as T-arms, strongly deviating from
the consensus cloverleaf. The single tRNA nucleotidyltransferase of this organism is fully active on
armless tRNAs, while the human counterpart is not able to add a complete CCA-end. Transplanting
single regions of the Romanomermis enzyme into the human counterpart, we identified a beta-turn
element of the catalytic core that—when inserted into the human enzyme—confers full CCA-adding
activity on armless tRNAs. This region, originally identified to position the 30
-end of the tRNA
primer in the catalytic core, dramatically increases the enzyme’s substrate affinity. While conventional
tRNA substrates bind to the enzyme by interactions with the T-arm, this is not possible in the case of
armless tRNAs, and the strong contribution of the beta-turn compensates for an otherwise too weak
interaction required for the addition of a complete CCA-terminus. This compensation demonstrates
the remarkable evolutionary plasticity of the catalytic core elements of this enzyme to adapt to
unconventional tRNA substrates.
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