Research Institute, National Cancer Center, Goyang-si, Korea.
Department of Bioengineering, Hanyang University, Seoul, Korea.
EMBO Rep. 2021 Jun 4;22(6):e51323. doi: 10.15252/embr.202051323. Epub 2021 May 2.
In eukaryotic cells, mitochondria are closely tethered to the endoplasmic reticulum (ER) at sites called mitochondria-associated ER membranes (MAMs). Ca ion and phospholipid transfer occurs at MAMs to support diverse cellular functions. Unlike those in yeast, the protein complexes involved in phospholipid transfer at MAMs in humans have not been identified. Here, we determine the crystal structure of the tetratricopeptide repeat domain of PTPIP51 (PTPIP51_TPR), a mitochondrial protein that interacts with the ER-anchored VAPB protein at MAMs. The structure of PTPIP51_TPR shows an archetypal TPR fold, and an electron density map corresponding to an unidentified lipid-like molecule probably derived from the protein expression host is found in the structure. We reveal functions of PTPIP51 in phospholipid binding/transfer, particularly of phosphatidic acid, in vitro. Depletion of PTPIP51 in cells reduces the mitochondrial cardiolipin level. Additionally, we confirm that the PTPIP51-VAPB interaction is mediated by the FFAT-like motif of PTPIP51 and the MSP domain of VAPB. Our findings suggest that PTPIP51 is a phospholipid transfer protein with a MAM-tethering function.
在真核细胞中，线粒体在称为线粒体相关内质网膜 (MAMs) 的位点与内质网 (ER) 紧密连接。钙离子和磷脂在 MAMs 处转移以支持多种细胞功能。与酵母不同，人类 MAMs 处参与磷脂转移的蛋白质复合物尚未被鉴定。在这里，我们确定了 PTPIP51（PTPIP51_TPR）四肽重复结构域的晶体结构，PTPIP51 是一种线粒体蛋白，它在 MAMs 处与 ER 锚定的 VAPB 蛋白相互作用。PTPIP51_TPR 的结构显示出典型的 TPR 折叠，并且在结构中发现了对应于可能来自蛋白质表达宿主的未识别脂质样分子的电子密度图。我们揭示了 PTPIP51 在体外磷脂结合/转移，特别是磷脂酸方面的功能。细胞中 PTPIP51 的耗竭会降低线粒体心磷脂水平。此外，我们证实 PTPIP51-VAPB 相互作用是由 PTPIP51 的 FFAT 样基序和 VAPB 的 MSP 结构域介导的。我们的研究结果表明，PTPIP51 是一种具有 MAM 连接功能的磷脂转移蛋白。
