Panel A shows a diagram that presents the domain organization of human T T L L 5 and R P G R proteins. T T L L 5 includes domains such as the T T L catalytic core in blue, c M T B D in maroon, and C I D in green. R P G R has two isoforms: R P G R Default and R P G R O R F 15, both containing an R C C 1-like propeller domain in yellow. The sequence for the minimal B D peptide required for T T L L 5 targeting to R P G R is shown in magenta. Panel B shows a titration binding curve graph that shows the interaction profile between the peptide and the protein domain across increasing molar ratios. Panel C shows a ribbon structure that displays the protein–peptide complex in two orientations to visualize the overall binding interface. Panel D shows a magnified structural view highlighting labeled amino acid residues forming hydrophobic contacts at the interaction site. Panel E shows another close-up structural view that shows additional residues and hydrogen bond interactions stabilizing the protein-peptide interface.
A minimal C-terminal helix in the RPGR BD is sufficient for CID binding and intercalates into the CID helical bundle through a conserved aromatic network. (A) Domain organization of human TTLL5 and RPGR. TTL catalytic core, blue; cMTBD, maroon; CID, green. RCC1-like β-propeller domain in RPGR, yellow, with each repeat shown as a separate propeller blade. Sequence for the minimal BD peptide required for TTLL5 targeting to RPGR shown in magenta at the top. (B) ITC measurements of WT miniBD peptide titrated into CID. Best fit of n = 2 independent experimental replicates. (C) 2.8-Å X-ray crystal structure of human TTLL5 CID in complex with human RPGR miniBD (Table 1) shown in cartoon representation; CID, green; RPGR, magenta. (D and E) Key conserved hydrophobic interactions at the CID–BD interface. Solid black boxes around residue labels designate disease-associated mutations, dashed boxes designate mutations without disease annotation in the ClinVar database that we predict are pathogenic based on our structure. RPGR and TTLL5 are colored as in B; H-bonds are shown as dashed lines.