BINDING OF PERLECAN TO TRANSTHYRETIN IN-VITRO

Transthyretin is one of two specific proteins involved in the transpor t of thyroid hormones in plasma; it possesses two binding sites for se rum retinol-binding protein. In the present study we demonstrate that transthyretin also interacts in vitro with [S-35]sulphate-labelled mat erial from the medium of HepG2 cells. By using the same strategy as fo r purifying serum retinol-binding protein, [S-35]sulphate-labelled med ium was specifically eluted from a transthyretin-affinity column. Ion- exchange chromatography showed that the material was highly polyanioni c, and its size and alkali susceptibility suggested that it was a prot eoglycan. Structural analyses with chondroitinase ABC lyase and nitrou s acid revealed that approx; 20 % was chondroitin sulphate and 80% hep aran sulphate. Immunoprecipitation showed that the [S-35]sulphate-labe lled material contained perlecan. Further analysis by binding studies revealed specific and saturable binding of I-125-transthyretin to perl ecan-enriched Matrigel. Because inhibition of sulphation by treating H epG2 cells with sodium chlorate increased the affinity of the perlecan for transthyretin, and [H-3]heparin was not retained by the transthyr etin affinity column, the binding is probably mediated by the core pro tein and is not a protein-glycosaminoglycan interaction Because perlec an is released from transthyretin in water, the binding might be due t o hydrophobic interactions.