Binding of perlecan to transthyretin in vitro.
Transthyretin is one of two specific proteins involved in the transport of thyroid hormones in plasma; it possesses two binding sites for serum retinol-binding protein. In the present study we demonstrate that transthyretin also interacts in vitro with [35S]sulphate-labelled material from the medium of HepG2 cells. By using the same strategy as for purifying serum retinol-binding protein, [35S]sulphate-labelled medium was specifically eluted from a transthyretin-affinity column. Ion-exchange chromatography showed that the material was highly polyanionic, and its size and alkali susceptibility suggested that it was a proteoglycan. Structural analyses with chondroitinase ABC lyase and nitrous acid revealed that approx. 20% was chondroitin sulphate and 80% heparan sulphate. Immunoprecipitation showed that the [35S]sulphate-labelled material contained perlecan. Further analysis by binding studies revealed specific and saturable binding of 125I-transthyretin to perlecan-enriched Matrigel. Because inhibition of sulphation by treating HepG2 cells with sodium chlorate increased the affinity of the perlecan for transthyretin, and [3H]heparin was not retained by the transthyretin affinity column, the binding is probably mediated by the core protein and is not a protein-glycosaminoglycan interaction. Because perlecan is released from transthyretin in water, the binding might be due to hydrophobic interactions.
Smeland
S
S
Institute for Nutrition Research, University of Oslo, P.O. Box 1046, 0316 Oslo, Norway.
Kolset
S O
SO
Lyon
M
M
Norum
K R
KR
Blomhoff
R
R
D019812:Heparan Sulfate Proteoglycans; D006497:Heparan Sulfate / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D011228:Prealbumin / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D011509:Proteoglycans / Q000737:chemistry / Q000378:metabolism*
D019812:Heparan Sulfate Proteoglycans; D006497:Heparan Sulfate; D011228:Prealbumin; D011509:Proteoglycans; C071927:perlecan