Fig. 6: Structural basis for the exclusive roles of EF-G1_mt in tRNA translocation and EF-G2_mt in mitoribosome recycling.

a The presence of a substantially longer C-terminal α-helix (salmon) along with the presence of a unique CTE (blue), which is required for mitochondria tRNA translocation⁶, prevents the simultaneous binding of EF-G1_mt and RRF_mt (green) on the mitoribosome due to a major steric clash. Furthermore, any conformational repositioning the C-terminal α-helix of EF-G1_mt will result in direct steric clash with the H89 (orange) of 16S rRNA and the NTE of RRF_mt (pink). b Having a shorter C-terminal α-helix (red) and the absence of CTE allows the simultaneous binding of EF-G2_mt and RRF_mt (green) on the mitoribosome. c In EF-G1_mt⁶, the presence of two universally conserved glycine residues (dark green) at the tip of domain IV loop1 region (salmon) facilitates its insertion between the mRNA-tRNA duplex at the decoding center (DC) during EF-G1_mt-catalyzed translocation. d In EF-G2_mt, the second glycine of domain IV loop 1 region (red) is substituted by an aspartic acid (dark green) altering its conformation and flexibility, and thereby making its insertion into the DC during translocation unfavorable. e The boxed aa sequence corresponds to the loop 1 situated at the tip of domain IV, which is conserved between EF-G1_mt and the T. thermophilus EF-G. First of the two universally conserved loop 1 glycine residues (green) is substituted by an alanine in B. burgdorferi EF-G2, while the second one is replaced by an aspartic acid in EF-G2_mt.