Heegaard Niels H H, Roepstorff Peter, Melberg Steen G, Nissen Mogens H
Department of Autoimmunology, Statens Serum Institut, DK-2300 Copenhagen S, Denmark.
J Biol Chem. 2002 Mar 29;277(13):11184-9. doi: 10.1074/jbc.M108837200. Epub 2002 Jan 18.
beta(2)-Microglobulin, a small protein localized in serum and on cell surfaces, can adopt specific aggregating conformations that generate amyloid in tissues and joints as a complication to long-term hemodialysis. We characterize a proteolytic variant of beta(2)-microglobulin (cleaved after Lys(58)) that as a trimmed form (Lys(58) is removed) can be demonstrated in the circulation in patients with chronic disease. An unexpected electrophoretic heterogeneity of these two cleaved variants was demonstrated by capillary electrophoresis under physiological conditions. Each separated into a fast and a slow component while appearing homogeneous, except for a fraction of oxidized species detected by other techniques. The two components had different binding affinities for heparin and for the amyloid-specific dye Congo red, and the equilibrium between the two forms was dependent on solvent conditions. Together with analysis of the differences in circular dichroism, the results suggest that beta(2)-microglobulin cleaved after Lys(58) readily adopts two equilibrium conformations under native conditions. In the cleaved and trimmed beta(2)-microglobulin that appears in vivo, the less populated conformation is characterized by an increased affinity for Congo red. These observations may help elucidate why beta(2)-microglobulin polymerizes as amyloid in chronic hemodialysis and facilitate the search for means to inhibit this process.
β2-微球蛋白是一种存在于血清和细胞表面的小蛋白质，它可以形成特定的聚集构象，在组织和关节中产生淀粉样蛋白，这是长期血液透析的一种并发症。我们对β2-微球蛋白的一种蛋白水解变体（在赖氨酸58之后切割）进行了表征，这种经修剪的形式（赖氨酸58被去除）可以在慢性病患者的循环中检测到。在生理条件下，通过毛细管电泳证明了这两种切割变体存在意想不到的电泳异质性。除了通过其他技术检测到的一部分氧化物种外，每种变体在外观上均一，但都分离成一个快速组分和一个慢速组分。这两个组分对肝素和淀粉样蛋白特异性染料刚果红具有不同的结合亲和力，并且两种形式之间的平衡取决于溶剂条件。结合圆二色性差异分析，结果表明赖氨酸58之后切割的β2-微球蛋白在天然条件下很容易形成两种平衡构象。在体内出现的经切割和修剪的β2-微球蛋白中，较少出现的构象对刚果红的亲和力增加。这些观察结果可能有助于阐明为什么β2-微球蛋白在慢性血液透析中会聚合成淀粉样蛋白，并有助于寻找抑制这一过程的方法。
