Protein kinases PIKK family

The probes of this type were shown to selectively label at least 75% of human kinases in crude cell lysates, thus demonstrating their selectivity and promiscuity for kinases [101]. As a follow up, the labeled kinases were subjected to proteolytic digestion, and the biotinylated peptides purified on avidin beads and analyzed by LC-MS/MS. This analysis demonstrated that the site of probe labeling was indeed the conserved active-site lysine as predicted. In contrast to the promiscuity demonstrated by the acyl phosphate probes, several selective covalent inhibitors of protein kinases have been used as ABPP probes. Wortmannin is a natural product derived from the fungus Penicillium funiculosum. It is a potent and specific covalent inhibitor of phosphoinositide 3-kinase (PI3K) and the PI3K-related kinase (PIKK) families [102, 103]. The use of natural products in relation to ABPP is covered by Breinbauer et al. [104]. 

The invariant SQ motif in the C-terminus of H2AX is a consensus sequence for the 3 kinases belonging to the PIKK family, namely ATM, DNA-PK and ATR (Stiff et al, 2004). These kinases are involved in DNA repair. ATM [ataxia telangiectasia (A-T) mutated protein] is a crucial kinase for the signal transduction DSB pathway (Savitsky et al, 1995) and it is widely accepted that ATM is the major kinase involved in the in vivo phosphorylation of H2AX (Burma et al, 2001 Fernandez-Capetillo et al, 2002 Redon et al, 2002). The two other kinases were also associated with the generation y-H2AX, but they appeared not to be dominant (Redon et al, 2002 Stiff et al, 2004). 

B. Master Switch PIKK Family of Protein Kinases. 110... 

Members of the PIKK family are not the only protein kinases involved in DNA damage response. Two other protein kinases, Ghkl and Ghk2, are also conserved through evolution and play important roles in regelating DNA damage responses (Bartek and Lukas, 2003). 

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