Substrate-specific adapter of a BCR (BTB-CUL3-RBX1) E3 ubiquitin ligase complex that acts as a key regulator of skeletal muscle development (PubMed:25940086). The BCR(KLHL40) complex acts by mediating ubiquitination and degradation of TFDP1, thereby regulating the activity of the E2F:DP transcription factor complex (PubMed:25940086). 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 (PubMed:24960163). Component of the BCR(KLHL40) E3 ubiquitin ligase complex, at least composed of CUL3, KLHL40 and RBX1 (PubMed:24361185). Interacts with LMOD3 (PubMed:24960163). Specifically expressed in skeletal muscles in embryonic, neonatal and adults (PubMed:24960163, PubMed:25940086). Expressed in various types of muscles, including extensor digitorum longus, gastrocnemius, soleus, diaphragm, masseter and heart (at protein level). Not detected in brain, liver and lung (at protein level). Absent early during embryogenesis (7 dpc), present at the middle stage (11 dpc) and highly expressed at the later stages (15 dpc and 17 dpc) (PubMed:24361185). Specifically expressed in the somites at 11.5 dpc and in the skeletal muscle at 15.5 dpc (PubMed:24361185). Up-regulated during myogenic differentiation (PubMed:24361185). Induced during the differentiation of myoblasts into myotubes (PubMed:23746549). Neonates are normal in size at birth and were born with the expected Mendelian ratio (PubMed:24960163, PubMed:25940086). They however fail to gain weight and do not survive to weaning (PubMed:24960163, PubMed:25940086). Defects are due to smaller muscle fibers and a disorganized sarcomeric structure (PubMed:24960163, PubMed:25940086). Belongs to the KLHL40 family.