Figure 2.

(a) Three-dimensional representation of the human GUF1 (light gray) and its CTD (white) in contact with a tRNA in the A-site of the ribosome. The different domains of the tRNA are color-coded: CCA 3′ (yellow), acceptor stem (purple), T-loop (green), D-loop (red), and anticodon loop (turquoise). The A609 residue is highlighted in yellow. (b) Three-dimensional model of the GUF1 tRNA-binding moiety (white) bound to the tRNA acceptor stem (purple) and D-loop (red). The T8 and A14 nucleotidic positions that are unconstrained in human mitochondrial tRNAs are emphasized (see text for details). The alanine 609 residue (highlighted in yellow) is located on the external beta-strand within the KIIARETV stretch (defined as ‘contact 2' in Connell et al²⁸), close to the evolutionary conserved glutamine (Q600), branched hydrophobic (I607) and Arginine (R610) residues. Their sidechains form a tightly packed motif that might be important for the proper recognition of the tRNA in the region located between the acceptor stem and the D-loop. The T-loop and part of the anticodon loop are indicated in green and turquoise, respectively. (c) The addition of a hydroxyl group at position 609 (p.(A609S) variant; compare with panel (b)) results in a bulkier residue, which might interfere with the tRNA acceptor stem by modifying the ‘contact 2' moiety. For color codes, see panel (b).