Fig. 4. Model of Mec1 activation by Dpb11.
(A) Sequence characteristics of the Mec1
and ATR activators in different species.
The unstructured AAD domain harbors high-abundance hydrophobic residues (green) and
contains essential aromatic amino acids (red) as
well as consecutive acidic patches (yellow).
(B and C) Cartoon of Mec1 activation showing
how the opening up of the active site leads
to full kinase activity. (B) Mec1 active site
before AAD binding; (C) tethering of
AAD onto the PRD, which could trigger
conformational changes destabilizing the
hydrophobic interaction between Phe2244 of the
activation loop and Met2312 in the PRD. The
resulting movement of the activation and
catalytic loops may open up the active site,
culminating in full kinase activity.
Fig. 3. The active site of Mec1. (A) Detailed view of the active site. The
color scheme of the N-lobe, C-lobe, and PRD is the same as in Fig. 1.
The activation loop (cyan), the catalytic loop (orange), the P-loop
(green), and the ka1 helix (purple) are labeled. The critical residues in the
catalytic and activation loops and the contact between Phe2244 and
Met2312 are highlighted. (B) Two other views of the active site, highlighting
the supersecondary structures that enclose the active site. The activation
and catalytic loops are besieged by the FATC and PRD. The high-abundance
basic residues in the PRD are labeled. A blue star denotes the position of
Lys2589 of human ATR. (C) Enlarged view of the Bridge domain, with one
helix of the HEAT 32R colored in red. (D) The interfaces of the a-solenoid
with the FAT and kinase domains. Cryo-EM densities of the two extended
loops (linker and railing) of the Bridge are highlighted. The Ser1333 residue
in human ATR (corresponding to Thr1092 in Mec1) creating a hyperactive
kinase is shown in red. (E) The active site is marked by an adenosine
diphosphate (ADP; red) that was modeled using the m TOR-ADP structure
(PDB ID 4JSV). Two helices of the HEAT 32R extend toward the active