Wybenga-Groot Leanne E, McGlade C Jane
The Arthur and Sonia Labatt Brain Tumour Research Centre and Program in Cell Biology, The Hospital for Sick Children, 555 University Avenue, Toronto, ON M5G 1X8, Canada.
Cell Signal. 2013 Dec;25(12):2702-8. doi: 10.1016/j.cellsig.2013.08.040. Epub 2013 Sep 7.
The Src-like adaptor proteins (SLAP/SLAP2) are key components of Cbl-dependent downregulation of antigen receptor, cytokine receptor, and receptor tyrosine kinase signaling in hematopoietic cells. SLAP and SLAP2 consist of adjacent SH3 and SH2 domains that are most similar in sequence to Src family kinases (SFKs). Notably, the SH3-SH2 connector sequence is significantly shorter in SLAP/SLAP2 than in SFKs. To understand the structural implication of a short SH3-SH2 connector sequence, we solved the crystal structure of a protein encompassing the SH3 domain, SH3-SH2 connector, and SH2 domain of SLAP2 (SLAP2-32). While both domains adopt typical folds, the short SH3-SH2 connector places them in close association. Strand βe of the SH3 domain interacts with strand βA of the SH2 domain, resulting in the formation of a continuous β sheet that spans the length of the protein. Disruption of the SH3/SH2 interface through mutagenesis decreases SLAP-32 stability in vitro, consistent with inter-domain binding being an important component of SLAP2 structure and function. The canonical peptide binding pockets of the SH3 and SH2 domains are fully accessible, in contrast to other protein structures that display direct interaction between SH3 and SH2 domains, in which either peptide binding surface is obstructed by the interaction. Our results reveal potential sites of novel interaction for SH3 and SH2 domains, and illustrate the adaptability of SH2 and SH3 domains in mediating interactions. As well, our results suggest that the SH3 and SH2 domains of SLAP2 function interdependently, with implications on their mode of substrate binding.
Src 样衔接蛋白（SLAP/SLAP2）是造血细胞中 Cbl 依赖性下调抗原受体、细胞因子受体和受体酪氨酸激酶信号传导的关键组成部分。SLAP 和 SLAP2 由相邻的 SH3 和 SH2 结构域组成，其序列与 Src 家族激酶（SFK）最为相似。值得注意的是，SLAP/SLAP2 中的 SH3-SH2 连接序列比 SFK 中的明显短。为了了解短 SH3-SH2 连接序列的结构含义，我们解析了包含 SLAP2 的 SH3 结构域、SH3-SH2 连接区和 SH2 结构域的蛋白质（SLAP2-32）的晶体结构。虽然这两个结构域都采用典型的折叠方式，但短的 SH3-SH2 连接区使它们紧密结合。SH3 结构域的βe 链与 SH2 结构域的βA 链相互作用，形成了一个跨越蛋白质长度的连续β折叠片层。通过诱变破坏 SH3/SH2 界面会降低 SLAP-32 在体外的稳定性，这与结构域间结合是 SLAP2 结构和功能的重要组成部分一致。与其他显示 SH3 和 SH2 结构域直接相互作用的蛋白质结构不同，在那些结构中，要么肽结合表面被相互作用所阻碍，而 SH3 和 SH2 结构域的经典肽结合口袋是完全可及的。我们的结果揭示了 SH3 和 SH2 结构域新的相互作用潜在位点，并说明了 SH2 和 SH3 结构域在介导相互作用方面的适应性。此外，我们的结果表明 SLAP2 的 SH3 和 SH2 结构域相互依赖发挥功能，这对它们的底物结合模式有影响。
