Adelson D L, Alliegro M C, McClay D R
Duke University, Zoology Department, Durham, North Carolina 27706.
J Cell Biol. 1992 Mar;116(5):1283-9. doi: 10.1083/jcb.116.5.1283.
Hyalin is a large (ca. 350 x 10(3) kD by gel electrophoresis) molecule that contributes to the hyalin layer surrounding the sea urchin embryo. In previous work a mAb (McA Tg-HYL), specific for hyalin, was found to inhibit cell-hyalin adhesion and block morphogenesis of whole embryos (Adelson, D. L., and T. D. Humphreys. 1988. Development. 104:391-402). In this report, hyalin ultrastructure was examined via rotary shadowing. Hyalin appeared to be a filamentous molecule approximately 75-nm long with a globular "head" about 12 nm in diameter that tended to form aggregates by associating head to head. Hyalin molecules tended to associate with a distinct high molecular weight globular particle ("core"). In fractions containing the core particle often more than one hyalin molecule were seen to be associated with the core. The core particle maintained a tenacious association with hyalin throughout purification procedures. The site(s) of McA Tg-HYL binding to the hyalin molecule were visualized by decorating purified hyalin with the antibody and then rotary shadowing the complex. In these experiments, McA Tg-HYL attached to the hyalin filament near the head region in a pattern suggesting that more than one antibody binding site exists on the hyalin filament. From the ultrastructural data and from the cell adhesion data presented earlier we conclude that hyalin is a filamentous molecule that binds to other hyalin molecules and contains multiple cell binding sites. Attempts were made to demonstrate the existence of lower molecular weight hyalin precursors. Whilst no such precursors could be identified by immunoprecipitation of in vivo labeled embryo lysates, immunoprecipitation of in vitro translation products suggested such precursors (ca 40 x 10(3) kD) might exist.
透明蛋白是一种大分子（凝胶电泳显示约为350×10³kD），它构成海胆胚胎周围的透明层。在之前的研究中，发现一种针对透明蛋白的单克隆抗体（McA Tg - HYL）能抑制细胞与透明蛋白的黏附并阻断整个胚胎的形态发生（Adelson, D. L., and T. D. Humphreys. 1988. Development. 104:391 - 402）。在本报告中，通过旋转投影法对透明蛋白的超微结构进行了研究。透明蛋白似乎是一种丝状分子，长约75纳米，有一个直径约12纳米的球状“头部”，倾向于通过头对头结合形成聚集体。透明蛋白分子倾向于与一种独特的高分子量球状颗粒（“核心”）结合。在含有核心颗粒的组分中，经常可以看到不止一个透明蛋白分子与核心结合。在整个纯化过程中，核心颗粒与透明蛋白保持着紧密的结合。通过用抗体修饰纯化后的透明蛋白，然后对复合物进行旋转投影，观察到McA Tg - HYL与透明蛋白分子的结合位点。在这些实验中，McA Tg - HYL以一种模式附着在透明蛋白丝靠近头部的区域，这表明透明蛋白丝上存在不止一个抗体结合位点。根据超微结构数据和之前给出的细胞黏附数据，我们得出结论：透明蛋白是一种丝状分子，它能与其他透明蛋白分子结合并含有多个细胞结合位点。曾尝试证明低分子量透明蛋白前体的存在。虽然通过对体内标记胚胎裂解物进行免疫沉淀无法鉴定出此类前体，但对体外翻译产物的免疫沉淀表明可能存在此类前体（约40×10³kD）。
