Substrate-specific adapter of a BCR (BTB-CUL3-RBX1) E3 ubiquitin ligase complex that acts as a key regulator of skeletal muscle development (PubMed:23746549). The BCR(KLHL40) complex acts by mediating ubiquitination and degradation of TFDP1, thereby regulating the activity of the E2F:DP transcription factor complex (By similarity). Promotes stabilization of LMOD3 by acting as a negative regulator of LMOD3 ubiquitination; the molecular process by which it negatively regulates ubiquitination of LMOD3 is however unclear (By similarity). {ECO:0000250|UniProtKB:Q9D783, ECO:0000269|PubMed:23746549}. This is the function of KLHL40 (kelch like family member 40, Ensembl gene identifier ENSG00000157119).