Fig. 1.

Sequence and structural alignments of TRB family proteins. (A) Schematic representation of the conserved domains of TRBs from A. thaliana. Myb-like, Myb-like domain; H1/5-like, histone-like domain; coiled-coil, C-terminal domain. (B) Unrooted Maximum likelihood (ML) phylogenetic tree of Brassicaceae TRB proteins. The length of the branches are proportional, and the black dots indicate the position of TRB1-5 from A. thaliana. For a list of species, see Supplementary Table 2. (C) Multiple alignments of the Myb-like, H1/5-like and coiled-coil domains. The positions of α-helices or β-sheets of the uppermost or the lowermost sequence in each alignment are highlighted: bold, experimentally determined structures (cryo-EM or X-ray crystallography); thin, AlphaFold prediction. Human Telomeric repeat-binding factor 2 (hTRF2) and Xenopus laevis histone H1.0 (Xl H1.0-B) were used to show the most conserved amino acid (aa) residues. Amino acid shading indicates the following conserved amino acids: dark green, hydrophobic and aromatic; light green, polar; blue, basic; magenta, acidic; yellow, without side chain (glycine and proline). The aa of hTRF2 that mediate intermolecular contacts between telomeric DNA and hTRF2 are marked with an asterisk. (D) Structural models of Myb-like, H1/5-like and coiled-coil domains. AlphaFold protein structure predictions deposited in the EMBL database were used (Varadi et al. 2022). The three-dimensional model of the Myb-like domain fits best the hTRF2-DNA interaction structure (PDB: 1WOU) (Court et al. 2005). The structure of the histone-like domain is most similar to X. laevis histone H1 structure (PDB: 5NL0) (Bednar et al. 2017). The positions of the aa of hTRF2 that mediate intermolecular contacts between telomeric DNA and hTRF2 are marked with an asterisk