Dowbenko D, Watson S R, Lasky L A
Department of Immunology, Genentech, Inc., South San Francisco, California 94080.
J Biol Chem. 1993 Jul 5;268(19):14399-403.
Recently we described the isolation of a mouse cDNA clone encoding a mucin-like endothelial glycoprotein that appears to function as an adhesive ligand for L selectin. This ligand has been named GlyCAM 1 (Gly-cosylation-dependent Cell Adhesion Molecule 1) because its adhesive interactions with the L selectin lectin domain require that the GlyCAM 1 polypeptide chain be appropriately modified with carbohydrates. These carbohydrate modifications include the addition of sialic acid as well as sulfate residues to O-linked carbohydrate side chains that are clustered in two serine/threonine-rich domains of the mucin. An additional interesting structure that may have relevance to the association of GlyCAM 1 with the lumenal surface of the endothelium was a potential amphipathic helix at the C terminus of the glycoprotein. In order to examine the importance of the postulated O-linked domains as well as the potential amphipathic helix, we have cloned the rat homologue of GlyCAM 1. The sequence of this clone reveals a serine/threonine-rich protein that is highly homologous with the mouse GlyCAM 1. As was found for the mouse GlyCAM 1, the rat homologue shows a clustering of these potential O-linked carbohydrate acceptors in two domains of the protein. Interestingly, many of the serines and threonines are found to be spaced identically in the two homologues, consistent with the possibility that both density and position of the O-linked side chains may be important for appropriate L selectin-mediated adhesion. In support of its postulated functional importance, the C-terminal potential amphipathic helix is conserved in the rat homologue. Finally, immunoprecipitation analysis of [35S]sulfate-labeled rat lymph nodes with either a mouse L selectin IgG chimera or a peptide antiserum directed against a relatively conserved portion of mouse GlyCAM 1 demonstrates a approximately 45-kDa sulfated ligand in rat lymph nodes that is analogous to that previously described for mouse lymph nodes.
最近，我们描述了一个小鼠cDNA克隆的分离过程，该克隆编码一种粘蛋白样内皮糖蛋白，它似乎作为L选择素的粘附配体发挥作用。这种配体被命名为GlyCAM 1（糖基化依赖性细胞粘附分子1），因为它与L选择素凝集素结构域的粘附相互作用要求GlyCAM 1多肽链用碳水化合物进行适当修饰。这些碳水化合物修饰包括在粘蛋白富含丝氨酸/苏氨酸的两个结构域中聚集的O-连接碳水化合物侧链上添加唾液酸以及硫酸根残基。糖蛋白C末端的一个潜在两亲性螺旋是另一个可能与GlyCAM 1与内皮腔表面结合相关的有趣结构。为了研究假定的O-连接结构域以及潜在两亲性螺旋的重要性，我们克隆了GlyCAM 1的大鼠同源物。该克隆的序列揭示了一种富含丝氨酸/苏氨酸的蛋白质，它与小鼠GlyCAM 1高度同源。正如在小鼠GlyCAM 1中发现的那样，大鼠同源物在蛋白质的两个结构域中显示出这些潜在O-连接碳水化合物受体的聚集。有趣的是，发现两个同源物中的许多丝氨酸和苏氨酸间距相同，这与O-连接侧链的密度和位置可能对适当的L选择素介导的粘附很重要的可能性一致。为了支持其假定的功能重要性，C末端潜在两亲性螺旋在大鼠同源物中是保守的。最后，用小鼠L选择素IgG嵌合体或针对小鼠GlyCAM 1相对保守部分的肽抗血清对[35S]硫酸盐标记的大鼠淋巴结进行免疫沉淀分析，结果表明大鼠淋巴结中有一种约45 kDa的硫酸化配体，类似于先前在小鼠淋巴结中描述的那种。
