The 67 kDa spliced variant of beta-galactosidase serves as a reusable protective chaperone for tropoelastin

Numerous cell types express the 67 kDa galactolectin related to the alternatively spliced variant of beta-galactosidase. This 67 kDa protein, while present on cell surfaces, mediates cell contacts with elastin, laminin and collagen type IV. In elastin-producing tissues, the 67 kDa protein also co-localizes with intracellular tropoelastin and mature elastic fibres. We have established that this elastin binding protein (EBP) serves as a molecular chaperone for tropoelastin. The EBP binds this highly hydrophobic and unglycosylated ligand intracellularly, protecting it from intracellular self aggregation and premature proteolytic degradation, and mediates its orderly assembly upon the microfibrillar scaffold. While some of this protein is incorporated as a permanent component of elastic fibres, most of the EBP, after extracellular dissociation from its ligand, recycles back to the intracellular endosomal compartment and re-associates with the newly synthesized tropoelastin. We suggest that recycling of this reusable shuttle protein is imperative for the effective extracellular deposition of insoluble elastin.