Structure of the EMMPRIN N-terminal domain 1: Dimerization via β-strand swapping
Structure of the EMMPRIN N-terminal domain 1: Dimerization via β-strand swapping
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DOI：
10.1002/prot.22577
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发表时间：
2009-12-01
影响因子：
2.9
通讯作者：
Gilliland, Gary L.
中科院分区：
文献类型：
--
作者：
Luo, Jinquan;Teplyakov, Alexey;Gilliland, Gary L.
细胞外基质金属蛋白酶诱导物（EMMPRIN），也称为Hab 18 G、CD 147、Basigin、M6和神经皮素，是在各种细胞类型和许多癌细胞的表面上表达的膜糖蛋白。EMMPRIN刺激邻近的成纤维细胞和肿瘤细胞产生基质金属蛋白酶，并在肿瘤侵袭和转移、血管生成、精子发生和受精、细胞-细胞粘附和通讯以及其他生物学过程中发挥重要作用（综述见参考文献1和其中的参考文献）。结果表明，EMMPRIN胞外结构域（ECD），其结构上属于IgG超家族，可以形成同源寡聚体的顺式依赖的方式和N-末端结构域1（残基22-101）是必要的，足以介导这种相互作用。在大肠杆菌中表达的重组人EMMPRIN（Hab 18 G/CD 147）的ECD晶体结构。大肠杆菌中以2.8埃的分辨率报道（Yu等，2008）。该构建体由成熟蛋白的残基22-205组成，并且具有N-末端IgC 2结构域（ND 1，残基22-101）和C-末端IgC 2结构域（ND 2，残基107-205）。两个结构域通过五个氨基酸残基的接头连接，该接头构成两个结构域之间的柔性铰链。该晶型在不对称单元中具有四个分子拷贝，每个拷贝具有从121{sup o}到144{sup o}变化的不同的畴间角。这两个结构域各自具有保守的二硫键，并且都由两个{β}-片层组成，所述两个{β}-片层分别由ND 1和ND 2的EBA和GFCC链以及DEBA和AGFCC链形成。基于该结构中的晶体堆积，作者提出EMMPRIN ECD的两个IgG结构域之间的横向堆积代表了细胞粘附的潜在机制。在这里，我们报告了在哺乳动物细胞中表达的EMMPRIN ECD（ND 1）的N-末端结构域的2.0埃晶体结构。该结构域的整体结构与全长ECD中的结构非常相似。非常出乎意料的是，ND 1通过其最后一条β链（G链）的交换介导形成二聚体。β-链交换是3D结构域交换的一个子集，已发现其通过钙粘蛋白介导细胞-细胞粘附。3D结构域交换已被认为是蛋白质寡聚化、聚集、寡聚蛋白从单个结构域进化和淀粉样变性的机制。在结构域交换的蛋白质中，相同的结构元件参与最终的3D结构，因此单体和交换的寡聚体之间的总体能量差异很小。然而，由于转换经常经历展开状态，因此通常存在高能量屏障。也可能在新生多肽链折叠期间发生链交换。通常，交换铰链含有富含脯氨酸的基序，其通常处于高应变构象。结构域交换似乎是解决这种局部结构应变的策略。ND 1的交换铰链含有Pro-Glu-Pro三肽基序。这两个脯氨酸残基采用扩展的反式构象相比，顺式在全长ECD结构。脯氨酸顺反异构化可能是这种交换的驱动力。链交换二聚化可能是EMMPRIN ECD寡聚化及其顺式依赖的细胞-细胞粘附中的嗜同性相互作用的机制。
Extracellular matrix metalloproteinase inducer (EMMPRIN), also known as Hab18G, CD147, Basigin, M6, and neurothelin, is a membrane glycoprotein expressed on the surface of various cell types and many cancer cells. EMMPRIN stimulates adjacent fibroblasts and tumor cells to produce matrix metalloproteinases and plays an important role in tumor invasion and metastasis, angiogenesis, spermatogensis and fertilization, cell-cell adhesion and communication, and other biological processes (reviewed in Ref. 1 and references therein). It was demonstrated that the EMMPRIN extracellular domain (ECD), which structurally belongs to the IgG superfamily, can form homo-oligomers in a cis dependent manner and the N-terminal domain 1 (residues 22-101) was necessary and sufficient to mediate this interaction. The crystal structure of the ECD of recombinant human EMMPRIN (Hab18G/CD147) expressed in E. coli was reported at 2.8 {angstrom} resolution (Yu et al. 2008). The construct consists of residues 22-205 of the mature protein and has both an N-terminal IgC2 domain (ND1, residues 22-101) and a C-terminal IgC2 domain (ND2, residues 107-205). The two domains are joined by a five amino acid residue linker that constitutes a flexible hinge between the two domains. The crystal form has four copies of the molecule in the asymmetric unit, each of which has a different inter-domain angle that varies from 121{sup o} to 144{sup o}. The two domains each have a conserved disulfide bridge and both are comprised of two {beta}-sheets formed by strands EBA and GFCC, and DEBA and AGFCC for ND1 and ND2, respectively. Based on the crystal packing in this structure, the authors proposed that lateral packing between the two IgG domains of EMMPRIN ECD represents a potential mechanism for cell adhesion. Here we report the 2.0-{angstrom} crystal structure of the N-terminal domain of EMMPRIN ECD (ND1) expressed in mammalian cells. The overall structure of the domain is very similar to that in the full length ECD. Quite unexpectedly, ND1 forms a dimer mediated through the exchange of its last {beta}-strand (strand G). {beta}-strand swapping, which is a subset of 3D domain swapping, has been found to mediate cell-cell adhesion by cadherins. 3D domain swapping has been proposed to be a mechanism of protein oligomerization, aggregation, evolution of oligomeric proteins from single domains and amyloidogenesis. In domain swapped proteins, the same structural elements are involved in the final 3D structure, and so there is little overall energetic difference between the monomer and the swapped oligomers. However, there is often a high energy barrier for the conversion as it often goes through an unfolded state. It is also possible that strand-swapping occurs during folding of nascent polypeptide chains. Frequently, the exchange hinges contain proline-rich motifs which are often in high strain conformations. Domain swapping appears to be a strategy to resolve such local structural strain. The exchange hinge of ND1 contains a Pro-Glu-Pro tripeptide motif. Both of the proline residues adopt extended trans conformations, when compared with cis in the full-length ECD structure. Proline cis-trans isomerization may be the driving force for this exchange. Strand-exchanged dimerization may be a mechanism for the oligomerization of EMMPRIN ECD and its cis-dependent homophilic interactions in cell-cell adhesion.