Witt D P, Lander A D
Glycan Pharmaceuticals, Inc., Cambridge, Massachusetts 02139.
Curr Biol. 1994 May 1;4(5):394-400. doi: 10.1016/s0960-9822(00)00088-9.
Specificity in leukocyte trafficking is likely to depend on sequential interactions between various cell-type-specific leukocyte adhesion molecules, such as selectins and integrin ligands, and leukocyte-activating factors. A major class of leukocyte-activating factors, the chemokines, are soluble polypeptides that bind glycosaminoglycans, the polysaccharide components of cell-surface and extracellular-matrix proteoglycans. It has been suggested that cell-surface glycosaminoglycans of the heparin/heparan sulfate class mediate the presentation of chemokines to leukocytes by vascular endothelial cells. We investigated the possibility that specificity exists in the recognition of particular heparin/heparan sulfate structures by chemokines, by studying the binding of four members of the chemokine superfamily to heparin and heparan sulfate.
Using affinity co-electrophoresis we found that interleukin-8 preferentially bound a subfraction of heparin that also showed increased affinity for melanoma growth stimulating activity (also known as MGSA, GRO or GRO alpha). This same subfraction of heparin, however, was not significantly preferentially bound by platelet factor 4 or neutrophil activating factor-2. Subsequent analysis of the three-dimensional structures of these chemokines indicated that their ability to discriminate among heparin subspecies correlates with the presence of paired glutamic acid residues within the putative glycosaminoglycan-binding site of the chemokine. This observation led to predictions about the relative affinities of heparan sulfate for interleukin-8 and platelet factor 4, predictions that were confirmed by further binding assays.
Chemokines can bind selectively to subsets of heparin/heparan sulfate glycosaminoglycans, raising the possibility that glycosaminoglycans participate in determining the specificity of leukocyte recruitment in vivo.
白细胞迁移的特异性可能取决于多种细胞类型特异性白细胞黏附分子（如选择素和整合素配体）与白细胞激活因子之间的顺序相互作用。一大类白细胞激活因子——趋化因子，是可结合糖胺聚糖（细胞表面和细胞外基质蛋白聚糖的多糖成分）的可溶性多肽。有人提出，肝素/硫酸乙酰肝素类的细胞表面糖胺聚糖介导血管内皮细胞向白细胞呈递趋化因子。我们通过研究趋化因子超家族的四个成员与肝素和硫酸乙酰肝素的结合，调查了趋化因子识别特定肝素/硫酸乙酰肝素结构时存在特异性的可能性。
使用亲和共电泳，我们发现白细胞介素-8优先结合肝素的一个亚组分，该亚组分对黑素瘤生长刺激活性（也称为MGSA、GRO或GROα）也表现出增加的亲和力。然而，血小板因子4或中性粒细胞激活因子-2对肝素的这个相同亚组分并没有明显的优先结合。随后对这些趋化因子三维结构的分析表明，它们区分肝素亚类的能力与趋化因子假定的糖胺聚糖结合位点内成对谷氨酸残基的存在相关。这一观察结果导致了关于硫酸乙酰肝素对白细胞介素-8和血小板因子4相对亲和力的预测，这些预测通过进一步的结合试验得到了证实。
趋化因子可以选择性地结合肝素/硫酸乙酰肝素糖胺聚糖的亚群，这增加了糖胺聚糖参与体内白细胞募集特异性决定的可能性。
