Structural requirements regulate endoproteolytic release of the L-selectin (CD62L) adhesion receptor from the cell surface of leukocytes.
Structural requirements regulate endoproteolytic release of the L-selectin (CD62L) adhesion receptor from the cell surface of leukocytes.
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DOI：
10.1084/jem.182.2.519
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发表时间：
1995-08-01
期刊：
影响因子：
--
通讯作者：
Tedder TF
中科院分区：
文献类型：
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作者：
Chen A;Engel P;Tedder TF
L-选择素介导炎症部位血管内皮上的白细胞滚动和淋巴细胞向外周淋巴结的迁移。在白细胞活化后，L-选择素通过蛋白水解机制从细胞表面迅速脱落，所述蛋白水解机制切割膜近端细胞外区域中的受体。这个过程可能允许白细胞在进入组织之前从内皮表面快速脱离。在这项研究中，通过分析嵌合选择素分子和突变型L-选择素受体，研究了调节人L-选择素蛋白内切酶解释放的结构要求。嵌合选择素和胞质尾截短突变体的使用表明，细胞外膜近端的15个氨基酸的L-选择素的区域是必需的内切蛋白水解释放。在该近膜区域内引入丙氨酸扫描突变并不能阻止蛋白内切酶的释放，这表明特定的氨基酸基序不是切割的绝对要求。此外，在假定的主要裂解位点（K283-S284）内的改变导致受体的组成性内切蛋白水解释放或细胞活化诱导的脱落的抑制到不同程度。近膜区域的长度也是关键的，因为该区域的截断完全消除了蛋白内切酶的释放。因此，L-选择素的释放可能通过在受体的近膜区域内产生适当的三级构象来调节，所述三级构象允许被具有松弛序列特异性的膜结合内切蛋白酶识别，所述膜结合内切蛋白酶在离质膜特定距离处切割受体。这些观察结果表明，一个广义的蛋白质加工途径参与特定的跨膜蛋白的内切蛋白水解释放，这些跨膜蛋白在其切割位点处或附近具有广泛不同的一级序列。
L-selectin mediates leukocyte rolling on vascular endothelium at sites of inflammation and lymphocyte migration to peripheral lymph nodes. L- selectin is rapidly shed from the cell surface after leukocyte activation by a proteolytic mechanism that cleaves the receptor in a membrane proximal extracellular region. This process may allow rapid leukocyte detachment from the endothelial surface before entry into tissues. In this study, the structural requirements for regulation of human L-selectin endoproteolytic release were examined through analysis of chimeric selectin molecules and mutant L-selectin receptors. The use of chimeric selectins and a cytoplasmic tail truncation mutant demonstrated that the extracellular membrane-proximal 15-amino acid region of L-selectin is required for endoproteolytic release. The introduction of alanine-scanning mutations within this membrane- proximal region did not prevent endoproteolytic release, indicating that a specific amino acid motif was not an absolute requirement for cleavage. Furthermore, alterations within the putative primary cleavage site (K283-S284) resulted in either constitutive endoproteolytic release of the receptor or inhibition of cell activation-induced shedding to variable extents. The length of the membrane-proximal region was also critical since truncations of this region completely abolished endoproteolytic release. Thus, release of L-selectin is likely to be regulated by the generation of an appropriate tertiary conformation within the membrane-proximal region of the receptor which allows recognition by a membrane-bound endoprotease with relaxed sequence specificity that cleaves the receptor at a specific distance from the plasma membrane. These observations suggest a generalized protein-processing pathway involved in the endoproteolytic release of specific transmembrane proteins which harbor widely differing primary sequences at or neighboring their cleavage sites.