Extended Data Fig. 8: Structural details of the TBE, bridge loop and related activity assays.
From: Structure of active human telomerase with telomere shelterin protein TPP1
a, Structure of the single-stranded RNA nucleotides at the 5′ side of the template in complex with TERT RBD (colored as in Fig. 3a). Cryo-EM densities of TER nucleotides are overlayed on the structure as transparent surfaces. Only the first two template-adjacent nucleotides (G44U45) and P1b have strong densities in the cryo-EM map, whereas the intervening nucleotides show only weak density indicative of positional dynamics. b, Comparison of the TBE-TBEL-RBD structures from human (color) and Tetrahymena (gray, PDB: 7LMA) telomerase. c, G44 and U45 in the kedge anchor pocket of TERT RBD. The linear distance from the phosphate group of U38 to the phosphate group of G44 is about 21 Å. d, Detailed interactions between G44-U45 and TERT RBD. Intermolecular hydrogen bonds are shown as dashed yellow lines. e, Schematic of TER TBE-TBEL-template conformation when the template is at the +3 position as in our structure. f, Predicted TBE-TBEL-template conformation when the template is at the +6 position. TBEL nucleotides U38–40 would be fully stretched to span the distance (21 Å) from the TBE anchor to the kedge anchor. g, Comparison of the template–DNA duplex and surrounding structural elements of human (color) and Tetrahymena (gray, PDB: 7LMA) telomerase. Residues located on the tip of the bridge loop are shown as sticks. h, Telomerase activity assays with substitutions of hTERT K499 and/or H500. Gel is a representative from 2 independent experiments. i, Detailed interactions surrounding the entrance of template nucleotides. Side chains of key residues are indicated with corresponding Tetrahymena TERT residues in parentheses. j, Ribbon diagram of the template-DNA duplex and the bridge loop superimposed with cryo-EM densities (transparent surface).
