Gundacker D, Leys S P, Schröder H C, Müller I M, Müller W E
Institut für Physiologische Chemie, Abteilung Angewandte Molekularbiologie, Universität, Duesbergweg 6, D-55099 Mainz, Germany.
Glycobiology. 2001 Jan;11(1):21-9. doi: 10.1093/glycob/11.1.21.
Among the sponges (Porifera), the oldest group of metazoans in phylogenetic terms, the Hexactinellida is considered to have diverged earliest from the two other sponge classes, the Demospongiae and Calcarea. The Hexactinellida are unusual among all Metazoa in possessing mostly syncytial rather than cellular tissues. Here we describe the purification of a cell adhesion molecule with a size of 34 kDa (in its native form; 24 kDa after deglycosylation) from the hexactinellid sponge Aphrocallistes vastus. This adhesion molecule was previously found to agglutinate preserved cells and membranes in a non-species-specific manner (Müller, W. E. G., Zahn, R. K, Conrad, J., Kurelec, B., and Uhlenbruck, G. [1984] Cell adhesion molecules in the haxactinellid Aphrocallistes vastus: species-unspecific aggregationfactor. Differentiation, 26, 30--35). The fact that the aggregation process required Ca(2+) and was inhibited by bird's nest glycoprotein and D-galactose but not by D-mannose or N-acetyl-D-galactosamine suggests that this cell adhesion molecule is a C-type lectin. To test this assumption, two highly similar C-type lectins were cloned from A.vastus. The deduced polypeptides of the two cDNA species isolated classified these molecules as C-type lectins. The calculated M(r) of the 191 aa long sequences were 22,022 and 22,064, respectively. The C-type lectins showed highest similarity to C-type lectins (type-II membrane proteins) from higher metazoan phyla; these molecules are absent in non-Metazoa. The two sponge C-type lectins contain the conserved domains known from other C-type lectins (e.g., disulfide bonds, the amino acids known to be involved in Ca(2+)-binding, as well as the amino acids involved in the specificity of binding to D-galactose) and a hydrophobic N-terminal region. The N-terminal part of the purified C-type lectin was identical with the corresponding region of the deduced polypeptide from the cDNA. It is proposed that the A.vastus lectins might bind to the cell membrane by their hydrophobic segment and might interact with carbohydrate units on the surface of the other cells/syncytia.
在系统发育学中，海绵动物门（多孔动物门）是后生动物中最古老的类群，其中六放海绵纲被认为是最早从另外两个海绵纲，即寻常海绵纲和钙质海绵纲中分化出来的。六放海绵纲在所有后生动物中很不寻常，其组织大多是合胞体而非细胞结构。在此，我们描述了从六放海绵纲的巨大 Aphrocallistes 海绵中纯化出一种大小为 34 kDa（天然形式）的细胞黏附分子，去糖基化后为 24 kDa。此前发现这种黏附分子能以非物种特异性的方式凝集保存的细胞和细胞膜（Müller, W. E. G., Zahn, R. K, Conrad, J., Kurelec, B., and Uhlenbruck, G. [1984] 六放海绵纲 Aphrocallistes 中的细胞黏附分子：非物种特异性聚集因子。分化，26, 30 - 35）。聚集过程需要 Ca(2+)，并受到燕窝糖蛋白和 D - 半乳糖的抑制，但不受 D - 甘露糖或 N - 乙酰 - D - 半乳糖胺的抑制，这一事实表明这种细胞黏附分子是一种 C 型凝集素。为验证这一假设，从巨大 Aphrocallistes 中克隆了两种高度相似的 C 型凝集素。分离得到的两个 cDNA 物种推导的多肽将这些分子归类为 C 型凝集素。191 个氨基酸长序列计算得到的 M(r)分别为 22,022 和 22,064。这两种 C 型凝集素与来自高等后生动物门的 C 型凝集素（II 型膜蛋白）显示出最高的相似性；非后生动物中不存在这些分子。这两种海绵 C 型凝集素含有其他 C 型凝集素已知的保守结构域（例如二硫键、已知参与 Ca(2+)结合的氨基酸，以及参与与 D - 半乳糖结合特异性的氨基酸）和一个疏水的 N 端区域。纯化的 C 型凝集素的 N 端部分与 cDNA 推导多肽的相应区域相同。有人提出，巨大 Aphrocallistes 凝集素可能通过其疏水片段与细胞膜结合，并可能与其他细胞/合胞体表面的碳水化合物单元相互作用。
