Abstract
REV7, also termed mitotic arrest-deficient 2-like 2 (MAD2L2 or MAD2B), acts as an interaction module in a broad array of cellular pathways, including translesion DNA synthesis, cell cycle control, and nonhomologous end joining. Numerous REV7 binding partners have been identified, including the human small GTPase Ras-associated nuclear protein (RAN), which acts as a potential upstream regulator of REV7. Notably, the Shigella invasin IpaB hijacks REV7 to disrupt cell cycle control to prevent intestinal epithelial cell renewal and facilitate bacterial colonization. However, the structural details of the REV7-RAN and REV7-IpaB interactions are mostly unknown. Here, using fusion protein and rigid maltose-binding protein tagging strategies, we determined the crystal structures of these two complexes at 2.00-2.35 Å resolutions. The structures revealed that both RAN and IpaB fragments bind the "safety belt" region of REV7, inducing rearrangement of the C-terminal β-sheet region of REV7, conserved among REV7-related complexes. Of note, the REV7-binding motifs of RAN and IpaB each displayed some unique interactions with REV7 despite sharing consensus residues. Structural alignments revealed that REV7 has an adaptor region within the safety belt region that can rearrange secondary structures to fit a variety of different ligands. Our structural and biochemical results further indicated that REV7 preferentially binds GTP-bound RAN, implying that a GTP/GDP-bound transition of RAN may serve as the molecular switch that controls REV7's activity. These results provide insights into the regulatory mechanism of REV7 in cell cycle control, which may help with the development of small-molecule inhibitors that target REV7 activity.
Highlights
REV7, termed mitotic arrest– deficient 2-like 2 (MAD2L2 or MAD2B), acts as an interaction module in a broad array of cellular pathways, including translesion DNA synthesis, cell cycle control, and nonhomologous end joining
Previous structural studies have primarily focused on the REV7–3–1 complex in translesion DNA synthesis (TLS) (4, 9 –11, 20), and only recently has attention turned to related study of the REV7–CAMP complex in mitosis [21]
As the small GTPase Ras-associated nuclear protein (RAN) is a potential upstream regulator of REV7, we focused on structural study of the REV7–RAN interaction
Summary
A previous report showed that the C-terminal moiety (residues 157–216) of RAN is responsible for the interaction with REV7 in vivo. In the proline core region, Pro-180RAN stacks tightly into the hydrophobic pocket built up by Tyr-63, Phe-169, Pro-170, and Trp-171 of REV7 (Fig. 2, A and C), in which the backbone of A181RAN forms one hydrogen bonds with the backbone of Pro-170REV7, and the backbone of Leu182RAN forms another hydrogen bond with the hydroxy group in the side chain of Tyr-63REV7.
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