Varner J A
J Cell Sci. 1995 Sep;108 ( Pt 9):3119-26. doi: 10.1242/jcs.108.9.3119.
Constitutive, stable intercellular adhesion is one of the distinguishing properties of metazoans, of which the sponges (Phylum Porifera) are the most primitive representatives. In sponges, intercellular adhesion is mediated by the large proteoglycan-like cell agglutinating molecule 'aggregation factor', which binds to cell surfaces via an oligosaccharide moiety. Previous studies indicated that this aggregation factor binds to two proteins associated with the surface of sponge cells. One of these, a 68 kDa peripheral membrane protein, was isolated by affinity chromatography on aggregation factor conjugated to Sepharose. This monomeric 68 kDa glycoprotein plays a key role in sponge cell adhesion since it potently inhibits the binding of aggregation factor to cell surfaces and completely prevents aggregation factor-mediated cell adhesion. The 68 kDa aggregation factor ligand binds with high affinity to both aggregation factor (KD = 2 x 10(-9) M) and cell surfaces (KD = 6 x 10(-8) M) providing evidence that it serves as an intramolecular bridge between the aggregation factor molecule and a cell surface receptor. Therefore, this early metazoan protein may represent one of the earliest extracellular matrix adhesion proteins to have arisen in the course of metazoan evolution.
组成性的、稳定的细胞间黏附是后生动物的显著特性之一，其中海绵动物（多孔动物门）是最原始的代表。在海绵动物中，细胞间黏附由大型蛋白聚糖样细胞凝集分子“聚集因子”介导，该分子通过寡糖部分与细胞表面结合。先前的研究表明，这种聚集因子与两种与海绵细胞表面相关的蛋白质结合。其中一种是68 kDa的外周膜蛋白，通过在与琼脂糖偶联的聚集因子上进行亲和层析分离得到。这种单体的68 kDa糖蛋白在海绵细胞黏附中起关键作用，因为它能有效抑制聚集因子与细胞表面的结合，并完全阻止聚集因子介导的细胞黏附。68 kDa的聚集因子配体与聚集因子（解离常数KD = 2×10⁻⁹ M）和细胞表面（KD = 6×10⁻⁸ M）都具有高亲和力，这表明它作为聚集因子分子和细胞表面受体之间的分子内桥梁。因此，这种早期后生动物蛋白可能代表后生动物进化过程中最早出现的细胞外基质黏附蛋白之一。
