Members of the F-box protein family, such as FBXO40, are characterized by an approximately 40-amino acid F-box motif. SCF complexes, formed by SKP1 (MIM 601434), cullin (see CUL1; MIM 603134), and F-box proteins, act as protein-ubiquitin ligases. F-box proteins interact with SKP1 through the F box, and they interact with ubiquitination targets through other protein interaction domains.[7]
Fbxo40 in particular engages a unique substrate, IRS1, which is a protein in the IGF1 signaling pathway. In this way, Fbxo40 causes ubiquitination and degradation of IRS1, blocking further signaling downstream of the IGF1 receptor.[5]
