Fig. 2: Maturation of H89 by GTPBP10.

a, b Overview of the position of GTPBP5 and GTPBP10 and the mtLSU interface. Notable is the difference between the location of H89 and the L7/12 stalk base in the GTPase activating center (GAC) between both intermediates. Important ribosomal RNA elements and mitoribosomal protein uL16m have been labeled. c Close-up of the tip of H89 and its surrounding elements. The tip is located between the RNA helices H43 and H44 of the GAC, H91, and the junction between Obg and GTPase domains of GTPBP10. d Surface representation of GTPBP10 colored according to coulombic electrostatic potential using default settings (blue = positive (10), red = negative (−10)) in ChimeraX. Ribosomal RNA helices H89, H91 and the sarcin-ricin loop (SRL) are shown for reference. e GTPBP10 structural model shown in the same orientation as in panel (d). Organization and positioning of GTPase and Obg domains are highlighted and the non-hydrolysable nucleotide analog GMPPNP is modeled in its binding site. Important surrounding ribosomal RNA elements are shown. The GTPBP10-specific alpha helical element that aids H89 positioning is boxed and shown in more detail on the right. The corresponding sharpened and 5-times supersampled EM density has been included as isomesh at two thresholds (red = 3.2 σ, gray = 2.3 σ). f, g Position of the SRL and the L7/12 stalk base in intermediate 1 in comparison to the mature mtLSU (PDB 7QI4) or the GTPBP5-bound intermediate (PDB 7ODT). For intermediate 1, rRNA of is shown in light blue and its ribosomal protein uL11m in blue while the same elements are shown in gray for the mature mitoribosome (f) or the GTPBP5-bound intermediate (g). The displacement of the stalk base is highlighted with respect to uL11m using a black arrow. GTPBP10 contains an insertion (boxed in f) in its GTPase domain that would clash with a stalk base conformation present in the mature mitoribosome. GTPBP5 lacks this insertion (shown in g). h Same as f but the ribosomal protein uL11m and GTPBP10 have been removed for clarity. The location of the tip of H89 is moreover highlighted.