Structural basis for specific lipid recognition by CERT responsible for nonvesicular trafficking of ceramide
Structural basis for specific lipid recognition by CERT responsible for nonvesicular trafficking of ceramide
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DOI：
10.1073/pnas.0709191105
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发表时间：
2008-01-15
影响因子：
11.1
通讯作者：
Kato, Ryulichi
中科院分区：
文献类型：
--
作者：
Kudo, Norio;Kurnagai, Keigo;Kato, Ryulichi
在哺乳动物细胞中，神经酰胺在内质网中合成，并转移到高尔基体转化为鞘磷脂。神经酰胺转运以非囊泡方式发生，并由CERT介导，CERT是一种具有C-末端类固醇生成急性调节蛋白相关脂质转移（START）结构域的细胞溶质68-kDa蛋白。CERT START结构域有效地转移天然D-β-C-16-神经酰胺，但不能转移具有较长（C-20）酰胺-酰基链的脂质。神经酰胺特异性的分子机制，包括立体特异性识别和长度限制，还没有很好地理解。在这里，我们报告的晶体结构的CERT开始域在其apo形式和复杂的神经酰胺具有不同的酰基链长度。在这些复杂的结构中，一个神经酰胺分子被埋在一个长的两亲性空腔中。在空腔的远端，神经酰胺的酰胺和羟基与特定的氨基酸残基形成氢键网络，这些氨基酸残基在立体特异性神经酰胺识别中起关键作用。在神经酰胺分子的头部，没有额外的空间来容纳额外的庞大基团。神经酰胺的两个脂族链被空腔的疏水壁包围，其大小和形状决定了同源神经酰胺的长度限制。此外，局部高结晶B因子表明α-3和ω-1环可能作为门将神经酰胺并入腔中。因此，这些结构证明了CERT可以将神经酰胺与其他脂质类型区分开来但仍然识别多种神经酰胺的机制的结构基础。
in mammalian cells, ceramide is synthesized in the endoplasmic reticulum and transferred to the Golgi apparatus for conversion to sphingomyelin. Ceramide transport occurs in a nonvesicular manner and is mediated by CERT, a cytosolic 68-kDa protein with a C-terminal steroidogenic acute regulatory protein-related lipid transfer (START) domain. The CERT START domain efficiently transfers natural D-erythro-C-16-ceramide, but not lipids with longer (C-20) amide-acyl chains. The molecular mechanisms of ceramide specificity, both stereo-specific recognition and length limit, are not well understood. Here we report the crystal structures of the CERT START domain in its apo-form and in complex with ceramides having different acyl chain lengths. In these complex structures, one ceramide molecule is buried in a long amphiphilic cavity. At the far end of the cavity, the amide and hydroxyl groups of ceramide form a hydrogen bond network with specific amino acid residues that play key roles in stereo-specific ceramide recognition. At the head of the ceramide molecule, there is no extra space to accommodate additional bulky groups. The two aliphatic chains of ceramide are surrounded by the hydrophobic wall of the cavity, whose size and shape dictate the length limit for cognate ceramides. Furthermore, local high-crystallographic B-factors suggest that the alpha-3 and the Omega 1 loop might work as a gate to incorporate the ceramide into the cavity. Thus, the structures demonstrate the structural basis for the mechanism by which CERT can distinguish ceramide from other lipid types yet still recognize multiple species of ceramides.