Watson N, McGuire V, Alexander S
Division of Biological Sciences, University of Missouri, Columbia 65211.
J Cell Sci. 1994 Sep;107 ( Pt 9):2567-79. doi: 10.1242/jcs.107.9.2567.
The PsB glycoprotein in Dictyostelium discoideum is one of a diverse group of developmentally regulated, prespore-cell-specific proteins, that contain a common O-linked oligosaccharide. This post-translational modification is dependent on the wild-type modB allele. The PsB protein exists as part of a multiprotein complex of six different proteins, which have different post-translational modifications and are held together by both covalent and non-covalent interactions (Watson et al. (1993). J. Biol. Chem. 268, 22634-22641). In this study we have used microscopic and biochemical analyses to examine the cellular localization and function of the PsB complex during development. We found that the PsB complex first accumulates in prespore vesicles in slug cells and is secreted later during culmination and becomes localized to both the extracellular matrix of the apical spore mass of mature fruiting bodies and to the inner layer of the spore coat. The PsB associated with the spore coat is covalently bound by disulfide bridges. The PsB protein always exists in a multiprotein complex, but the composition of the PsB complex changes during secretion and spore maturation. Some of the PsB complex proteins have been identified as spore coat proteins. These data demonstrate that some of the proteins that form the spore coat exist as a preassembled precursor complex. The PsB complex is secreted in a developmentally regulated manner during the process of spore differentiation, at which time proteins of the complex, as well as additional spore coat proteins, become covalently associated in at least two forms of extracellular matrix: the interspore matrix and the spore coat. These and other studies show that proteins with modB dependent O-linked oligosaccharides are involved in a wide variety of processes underlying morphogenesis in this organism. These developmental processes are the direct result of cellular mechanisms regulating protein targeting, assembly and secretion, and the assembly of specific extracellular matrices.
盘基网柄菌中的PsB糖蛋白是一组受发育调控的、前孢子细胞特异性蛋白中的一种，这些蛋白含有共同的O-连接寡糖。这种翻译后修饰依赖于野生型modB等位基因。PsB蛋白作为一个由六种不同蛋白质组成的多蛋白复合物的一部分存在，这些蛋白质具有不同的翻译后修饰，并通过共价和非共价相互作用结合在一起（沃森等人（1993年）。《生物化学杂志》268，22634 - 22641）。在这项研究中，我们使用显微镜和生化分析来研究PsB复合物在发育过程中的细胞定位和功能。我们发现，PsB复合物首先在蛞蝓细胞的前孢子小泡中积累，随后在发育后期分泌，并定位于成熟子实体顶端孢子团的细胞外基质和孢子壁的内层。与孢子壁相关的PsB通过二硫键共价结合。PsB蛋白总是存在于一个多蛋白复合物中，但PsB复合物的组成在分泌和孢子成熟过程中会发生变化。一些PsB复合物蛋白已被鉴定为孢子壁蛋白。这些数据表明，一些构成孢子壁的蛋白以预先组装的前体复合物形式存在。在孢子分化过程中，PsB复合物以发育调控的方式分泌，此时复合物中的蛋白质以及其他孢子壁蛋白至少以两种细胞外基质形式共价结合：孢子间基质和孢子壁。这些以及其他研究表明，具有依赖modB的O-连接寡糖的蛋白质参与了该生物体形态发生的多种过程。这些发育过程是调节蛋白质靶向、组装和分泌以及特定细胞外基质组装的细胞机制的直接结果。
