Lysosomal membrane chaperone required to export cobalamin (vitamin B12) from the lysosome to the cytosol, allowing its conversion to cofactors (PubMed:19136951). Targets ABCD4 transporter from the endoplasmic reticulum to the lysosome (PubMed:27456980). Then forms a complex with lysosomal ABCD4 and cytoplasmic MMACHC to transport cobalamin across the lysosomal membrane (PubMed:25535791). Acts as an adapter protein which plays an important role in mediating and regulating the internalization of the insulin receptor (INSR) (By similarity). Involved in clathrin-mediated endocytosis of INSR via its interaction with adapter protein complex 2 (By similarity). Essential for the initiation of gastrulation and early formation of mesoderm structures during embryogenesis (By similarity). (Microbial infection) May play a role in the assembly of hepatitis delta virus (HDV). (Microbial infection) Interacts with hepatitis delta virus NES (HDAg-L). Interacts with ABCD4; this interaction induces the translocation of ABCD4 from the endoplasmic reticulum to the lysosome (PubMed:27456980,PubMed:28572511,PubMed:33845046). Interacts with ABCD4 and MMACHC; this interaction ensures the transport of cobalamin from the lysosome to the cytoplasm (PubMed:25535791). Interacts with INSR, adapter protein complex 2 and clathrin heavy chain (By similarity). Isoform 3 is expressed in liver. N-glycosylated. The disease is caused by variants affecting the gene represented in this entry. Belongs to the LIMR family. LMBRD1 subfamily.