Chaperone specifically assisting the folding of beta-propeller/EGF modules within the family of low-density lipoprotein receptors (LDLRs) (PubMed:15014448). Acts as a modulator of the Wnt pathway through chaperoning the coreceptors of the canonical Wnt pathway, LRP5 and LRP6, to the plasma membrane (PubMed:17488095). Essential for specification of embryonic polarity and mesoderm induction. Plays an essential role in neuromuscular junction (NMJ) formation by promoting cell-surface expression of LRP4 (By similarity). May regulate phagocytosis of apoptotic retinal pigment epithelium (RPE) cells (By similarity). Monomer. Interacts with LRP5; the interaction prevents LRP5 from forming aggregates and chaperones LRP6 to the plasma membrane (PubMed:17488095). Interacts with LRP6; the interaction prevents LRP6 from forming aggregates and chaperones LRP6 to the plasma membrane (PubMed:17488095). Interacts with LRP4; the interaction promotes glycosylation of LRP4 and its cell-surface expression (By similarity). Released from apoptotic cells and shed photoreceptor outer segments. The chaperone domain provides a folding template for proper folding of the beta-propeller (BP) domains of LRP5/6. The escort domain ensures LRP5/6 safe-trafficking from the ER to the Golgi by preventing premature ligand-binding. The disease is caused by variants affecting the gene represented in this entry. Belongs to the MESD family. Extended N-terminus.