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Catalytic domain of Ataxia Telangiectasia Mutated ATM is critical in the response to DNA double strand breaks (DSBs) caused by radiation. It is activated at the site of a DSB and phosphorylates key substrates that trigger pathways that regulate DNA repair and cell cycle checkpoints at the G1/S, S phase, and G2/M transition. Patients with the human genetic disorder Ataxia telangiectasia (A-T), caused by truncating mutations in ATM, show genome instability, increased cancer risk, immunodeficiency, compromised mobility, and neurodegeneration. A-T displays clinical heterogeneity, which is correlated to the degree of retained ATM activity. ATM contains a FAT (FRAP, ATM and TRRAP) domain, a catalytic domain, and a FATC domain at the C-terminus. It is a member of the phosphoinositide 3-kinase-related protein kinase (PIKK) subfamily. PIKKs have intrinsic serine/threonine kinase activity and are distinguished from other PKs by their unique catalytic domain, similar to that of lipid PI3K, and their large molecular weight (240-470 kDa). The ATM catalytic domain subfamily is part of a larger superfamily that includes the catalytic domains of other kinases such as the typical serine/threonine/tyrosine protein kinases (PKs), aminoglycoside phosphotransferase, choline kinase, and RIO kinases.
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