Kaname S, Ruoslahti E
Cancer Research Center, La Jolla Cancer Research Foundation, La Jolla, CA 92037, USA.
Biochem J. 1996 May 1;315 ( Pt 3)(Pt 3):815-20. doi: 10.1042/bj3150815.
The transforming growth factor-beta (TGF-beta) binding site in betaglycan, the type III TGF-beta receptor, has been variously assigned to the C-terminal half and N-terminal one-third of the extracellular domain. In this study, we show that there are at least two TGF-beta-binding sites in betaglycan. Bacterially expressed fragments bg 1,2 and bg3, which represent the N-terminal two-thirds and C-terminal one-third of betaglycan extracellular domain, both competed for the binding of 125I-TGF-beta to mink lung epithelial cells. 125I-bg1,2 bound to immobilized TGF-beta with an affinity about 4-fold higher than bg3 had. Both bg3 and bg1,2 enhanced the bioactivity of TGF-beta. The whole ectodomain of betaglycan was more active than either bg3 or bg1,2 in the assays. The binding of 125I-bg3 to TGF-beta was inhibited by bg1,2 and vice versa. The binding of 125I-bg3 and 125I-bg1,2 to TGF-beta was also inhibited by the small decorin family of proteoglycans. These results indicate that there are at least two binding sites for TGF-beta in betaglycan and that these sites recognize the same or overlapping sites in TGF-beta.
β聚糖（III型转化生长因子-β（TGF-β）受体）中的TGF-β结合位点，在胞外域的C端后半部分和N端三分之一处有不同的定位。在本研究中，我们表明β聚糖中至少有两个TGF-β结合位点。细菌表达的片段bg1,2和bg3，分别代表β聚糖胞外域的N端三分之二和C端三分之一，二者都能竞争125I-TGF-β与貂肺上皮细胞的结合。125I-bg1,2与固定化TGF-β的结合亲和力比bg3高约4倍。bg3和bg1,2都能增强TGF-β的生物活性。在实验中，β聚糖的整个胞外域比bg3或bg1,2更具活性。125I-bg3与TGF-β的结合受到bg1,2的抑制；反之亦然。125I-bg3和125I-bg1,2与TGF-β的结合也受到小分子核心蛋白聚糖家族蛋白聚糖的抑制。这些结果表明，β聚糖中至少有两个TGF-β结合位点，且这些位点识别TGF-β中相同或重叠的位点。
