Syntenin is an adaptor-like molecule that binds to the cytoplasmic domains of all four vertebrate syndecans. Syntenin-syndecan binding involves the C-terminal part of syntenin that contains a tandem of PDZ domains. Here we provide evidence that each PDZ domain of syntenin can interact with a syndecan. Isolated or combined mutations of the carboxylate binding lysines in the inter-betaAbetaB loops and of the alphaB1 residues in either one or both the PDZ domains of syntenin all reduce syntenin-syndecan binding in yeast two-hybrid, blot-overlay, and surface plasmon resonance assays. PDZ2 mutations have more pronounced effects on binding than PDZ1 mutations, but complete abrogation of syntenin-syndecan binding requires the combination of both the lysine and the alphaB1 mutations in both the PDZ domains of syntenin. Isothermal calorimetric titration of syntenin with syndecan peptide reveals the presence of two binding sites in syntenin. Yet, unlike a tandem of two PDZ2 domains and a reconstituted PDZ1+PDZ2 tandem, a tandem of two PDZ1 domains and isolated PDZ1 or PDZ2 domains do not interact with syndecan bait. We conclude to a co-operative binding mode whereby neither of these two PDZ domains is sufficient by itself but where PDZ2 functions as a "major" or "high affinity" syndecan binding domain, and PDZ1 functions as an "accessory" or "low affinity" syndecan binding domain. The paired, but not the isolated PDZ domains of syntenin bind also strongly to the immobilized cytoplasmic domains of neurexin and B-class ephrins. By inference, these data suggest a model whereby recruitment of syntenin to membrane surfaces requires two compatible types of bait that are in "synteny" (occurring together in location) and engages both PDZ domains of syntenin. The synteny of compatible bait may result from the assemblies and co-assemblies of syndecans and other similarly suited partners in larger supramolecular complexes. In general, an intramolecular combination of PDZ domains that are weak, taken individually, would appear to be designed to detect rather than drive the formation of specific molecular assemblies.

译文

Syntenin是一种衔接子样分子,与所有四种脊椎动物syndecans的细胞质结构域结合。Syntenin-syndecanbinding涉及syntenin的C端部分,其中包含串联的PDZ结构域。在这里,我们提供的证据表明,syntenin的每个PDZ结构域都可以与syndecan相互作用。Betaabetaab间环中的羧酸盐结合赖氨酸的分离或组合突变以及syntenin的一个或两个PDZ结构域中的alphaB1残基的分离或组合突变都减少了酵母双杂交,印迹覆盖和表面等离子体共振分析中的syntenin-syndecana结合。PDZ2突变对结合的影响比PDZ1突变更明显,但是syntenin-syndecan结合的完全废除需要在syntenin的两个PDZ结构域中同时结合赖氨酸和 αb1突变。用syndecan肽对syntenin进行等温量热滴定,发现syntenin中存在两个结合位点。然而,与两个PDZ2结构域的串联和重构的PDZ1 PDZ2串联不同,两个PDZ1结构域和分离的PDZ1或PDZ2结构域的串联不与syndeca诱饵相互作用。我们得出结论,这是一种合作结合模式,因此这两个PDZ结构域本身都不足够,但是PDZ2充当 “主要” 或 “高亲和力” syndecan结合域,而PDZ1充当 “附件” 或 “低亲和力” syndecan结合域。合成蛋白的配对但不是分离的PDZ结构域也与固定的neurexin和B类肾上腺素的胞质结构域紧密结合。通过推论,这些数据提出了一个模型,其中将syntenin募集到膜表面需要两种兼容类型的诱饵,它们处于 “synteny” (在位置上同时发生) 并与syntenin的两个PDZ结构域结合。相容诱饵的合并性可能是由较大的超分子复合物中syndecans和其他类似合适的伴侣的组装和共组装引起的。通常,单独使用弱的PDZ结构域的分子内组合似乎旨在检测而不是驱动特定分子组装体的形成。

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