Skip to main content
. 2022 Dec 8;50(22):13083–13099. doi: 10.1093/nar/gkac1137

Figure 4.

Figure 4.

L3MBTL3 adopts a distinct structure among RBPJ coregulators. (A) Structural alignment of RAM and RAM-like peptides bound to RBPJ shows a recurrent interaction conformation. RAM from the C. elegans Notch ortholog Lin12 (red), FHL1 (light blue), RITA1 (orange), SHARP (dark green) and L3MBTL3 (purple) all bind to the CSL BTD (green surface) as extended peptides. Shown as sticks are L3MBTL3 residues W64 and P67, as well as the corresponding conserved residues in other coregulators. Unlike other coregulators, the backbone of L3MBTL3 (purple) diverges structurally by forming a large bulge over the cavity joining the top and front of the BTD, which is denoted with an asterisk. (B) Structure based sequence alignment of L3MTBL3 with other BTD binding proteins. The conserved tryptophan residue of the hydrophobic tetrapeptide, which has the sequence -ΦWΦP- where Φ = hydrophobic residue, is boxed in black. In contrast to other coregulators, L3MBTL3 has a valine in the fourth position of the -ΦWΦP- instead of a proline, but has a proline immediately following this position (blue rectangle), which is conserved in RITA1, SHARP, and some Notch receptor orthologs. A60 aligns to the strongly conserved position, which requires small sidechain residues (red rectangle); however, this leads to L3MBTL3 having three threonine residues between the alanine and tryptophan, whereas all other coregulators only have two residues. (C) Top-down view of the RBP-ID N-terminus showing that the L3MBTL3 extrusion (purple) pushes its backbone out of alignment with respect to the other coregulators. (D) Aligned stick models of RAM-like peptides show the conserved positions of L3MBTL3 A60 and W64. T63 essentially realigns with the first hydrophobic tetrapeptide residues, forcing the T61/T62 dithreonine to create the structural bulge. (E) The crystal structure of L3MBTL3 Δ62 peptide (pink) bound to RBPJ demonstrates a complete realignment of L3MBTL3 with the other RAM-like peptides, in which L3MBTL3 adopts the β-strand interaction seen in RAM, FHL1 and RITA1.