The Dimeric Architecture of Checkpoint Kinases Mec1ATR and Tel1ATM Reveal a Common Structural Organization

Abstract

The phosphatidylinositol 3-kinase-related protein kinases are key regulators controlling a wide range of cellular events. The yeast Tel1 and Mec1·Ddc2 complex (ATM and ATR-ATRIP in humans) play pivotal roles in DNA replication, DNA damage signaling, and repair. Here, we present the first structural insight for dimers of Mec1·Ddc2 and Tel1 using single-particle electron microscopy. Both kinases reveal a head to head dimer with one major dimeric interface through the N-terminal HEAT (named after Huntingtin, elongation factor 3, protein phosphatase 2A, and yeast kinase TOR1) repeat. Their dimeric interface is significantly distinct from the interface of mTOR complex 1 dimer, which oligomerizes through two spatially separate interfaces. We also observe different structural organizations of kinase domains of Mec1 and Tel1. The kinase domains in the Mec1·Ddc2 dimer are located in close proximity to each other. However, in the Tel1 dimer they are fully separated, providing potential access of substrates to this kinase, even in its dimeric form.

Insights into Rad3 kinase recruitment from the crystal structure of the DNA damage checkpoint protein Rad26

“…The internal symmetry observed is most likely created by the Rad26 dimer that positions two opposing binding sites for Rad3 that are rotated 180°relative to each other. A very similar dimeric architecture was recently observed in a 3D reconstruction of the orthologs complex in yeast Mec1-Ddc2 (16). Based on the combined data, it is possible to suggest a model of how Rad3-Rad26 assembles into a heterotetrameric complex, in which the Rad26 dimer is the central scaffold binding two molecules of Rad3 through their HEAT domains (Fig.…”

The essential kinase ATR: ensuring faithful duplication of a challenging genome

“…( d ) Model of ATR activation. ATR–ATRIP forms a dimer of dimers 167 . TOPBP1 or ETAA1 AAD binding likely induces a conformational change in ATR that reduces the Km of ATR for its substrates and thereby activates ATR 168 .…”

Mec1ATR Autophosphorylation and Ddc2ATRIP Phosphorylation Regulates DNA Damage Checkpoint Signaling

“…Mec1 Autophosphorylation at Site S1964 Can Occur in trans Recent structural studies have suggested that budding yeast Mec1-Ddc2 exists as a homodimer of a heterodimer (Sawicka et al, 2016;Wang et al, 2017). Autophosphorylation of Mec1 could, therefore, happen in cis or in trans.…”

“…Under basal conditions, most Mec1 exists as a homodimer of a heterodimer with its binding partner Ddc2 ATRIP (Ball and Cortez, 2005;Sawicka et al, 2016). Upon induction of a DSB, the double-stranded DNA (dsDNA) ends are resected and coated with the single-stranded DNA (ssDNA) binding protein RPA (Alani et al, 1992;Zou and Elledge, 2003).…”