Functional characterization of a clinically significant variant of IGF1R (M1054I) - a critical residue involved in defining the binding of small molecules in the allosteric pocket of IGF1R.

IGF1R, a receptor tyrosine kinase, is crucial for cell growth, proliferation, and differentiation. Overexpression of IGF1R is linked to cancer and resistance to therapies, making it a target for drug development. Previously, we identified an allosteric binding pocket in IGF1R, which could be exploited for the development of IGF1R specific small molecule inhibitors. A recent study linked M1054I variant to growth defects and microcephaly. In this study, we functionally characterized M1054I to assess its effects on kinase activity, downstream signaling, and receptor structure. Replacing methionine with isoleucine at position 1054 leads to complete loss of kinase activity. Consequently, activation of downstream signaling molecules is significantly reduced in cells carrying the M1054I mutation. Structural analysis reveals that the mutation causes conformational changes in key conserved regions, particularly in the activation loop, compromising IGF1R's structural integrity and function. Additionally, the roles of residues Y987 and K1033 in regulating IGF1R functions were examined.