In tumors, C2 residue Asn345 is frequently mutated to lysine. Before the publication of the p110/niSH2
structure, the main function of C2 was thought to be promotion of the interaction of PI3K with the
membrane. Based on this assumption it was proposed that the mutation weakened the interaction of the
enzyme with the membrane, lessening the access to its substrate PIP2. The structure of the p110a/niSH2,
however, showed that these mutations have a different effect. Asn354 is at H-bonding distance of two
residues of the iSH2 domain of p85, Asn564 and Asp560; therefore its mutation affects the interaction ofp110a with iSH2. In agreement with this observation, a recent sequence of a glioblastoma cell line showed
that residues Asp560 and Asn564 of p85a are also highly mutated in tumors (Cancer Genome Atlas
Research Network, 2008). The effect of mutating these residues is equivalent to mutating Asn354 of
the C2 domain. Glu453Gln, another common C2 mutation, is also present at the interface between C2 and
iSH2 and most likely alters the interaction between the C2 domain of p110a and the iSH2 domain of p85a.
In tumors, C2 residue Asn345 is frequently mutated to lysine. Before the publication of the p110/niSH2structure, the main function of C2 was thought to be promotion of the interaction of PI3K with themembrane. Based on this assumption it was proposed that the mutation weakened the interaction of theenzyme with the membrane, lessening the access to its substrate PIP2. The structure of the p110a/niSH2,however, showed that these mutations have a different effect. Asn354 is at H-bonding distance of tworesidues of the iSH2 domain of p85, Asn564 and Asp560; therefore its mutation affects the interaction ofp110a with iSH2. In agreement with this observation, a recent sequence of a glioblastoma cell line showedthat residues Asp560 and Asn564 of p85a are also highly mutated in tumors (Cancer Genome AtlasResearch Network, 2008). The effect of mutating these residues is equivalent to mutating Asn354 ofthe C2 domain. Glu453Gln, another common C2 mutation, is also present at the interface between C2 andiSH2 and most likely alters the interaction between the C2 domain of p110a and the iSH2 domain of p85a.
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