Crystal Structure of Geranylgeranyl Pyrophosphate Synthase (CrtE) Involved in Cyanobacterial Terpenoid Biosynthesis
Crystal Structure of Geranylgeranyl Pyrophosphate Synthase (CrtE) Involved in Cyanobacterial Terpenoid Biosynthesis
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DOI：
10.3389/fpls.2020.00589
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发表时间：
2020-05-25
影响因子：
5.6
通讯作者：
Nixon, Peter J.
中科院分区：
文献类型：
--
作者：
Feng, Yuchi;Morgan, R. Marc L.;Nixon, Peter J.
蓝细菌是进行产氧光合作用的光合原核生物。由于它们能够利用阳光的光子能量将二氧化碳固定到生物质中，蓝藻是可持续生产萜类化合物（也称为类异戊二烯）的有希望的宿主，这是一种具有先进生物燃料和高价值化学品潜力的多种天然产物。然而，蓝藻酶参与生物合成的萜烯前体，需要使更复杂的萜类化合物的特点很差。在这里，我们表明，预测的II型异戊烯基转移酶CrtE编码的模式蓝藻聚球藻属PCC 7002是同源二聚体，能够合成C20-香叶基香叶基焦磷酸（GGPP）从C5-异戊烯焦磷酸（IPP）和C5-二甲基烯丙基焦磷酸（DMAPP）。晶体结构的CrtE解决了2.7埃的分辨率揭示了一个强的结构相似性的大亚基异二聚体香叶基香叶基焦磷酸合酶1从拟南芥与每个亚基含有14个螺旋。使用诱变，我们证实，第四和第五个氨基酸（Met-87和Ser-88）之前的第一个保守的富含谷氨酸基序（FARM）发挥重要作用，在控制链延长。虽然WT酶特异性产生GGPP，但变体M87F和S88Y仅能产生C15-法尼基焦磷酸（FPP），表明具有大侧链的残基阻碍产物延伸。相比之下，用较小的Ala残基替换M87允许形成较长的C25-香叶基法尼基焦磷酸（GFPP）产物。总的来说，我们的研究结果提供了新的结构和功能信息的蓝藻CrtE酶，可能会导致开发的改进蓝藻平台萜类化合物的生产。
Cyanobacteria are photosynthetic prokaryotes that perform oxygenic photosynthesis. Due to their ability to use the photon energy of sunlight to fix carbon dioxide into biomass, cyanobacteria are promising hosts for the sustainable production of terpenoids, also known as isoprenoids, a diverse class of natural products with potential as advanced biofuels and high-value chemicals. However, the cyanobacterial enzymes involved in the biosynthesis of the terpene precursors needed to make more complicated terpenoids are poorly characterized. Here we show that the predicted type II prenyltransferase CrtE encoded by the model cyanobacterium Synechococcus sp. PCC 7002 is homodimeric and able to synthesize C20-geranylgeranyl pyrophosphate (GGPP) from C5-isopentenyl pyrophosphate (IPP) and C5-dimethylallyl pyrophosphate (DMAPP). The crystal structure of CrtE solved to a resolution of 2.7 angstrom revealed a strong structural similarity to the large subunit of the heterodimeric geranylgeranyl pyrophosphate synthase 1 from Arabidopsis thaliana with each subunit containing 14 helices. Using mutagenesis, we confirmed that the fourth and fifth amino acids (Met-87 and Ser-88) before the first conserved aspartate-rich motif (FARM) play important roles in controlling chain elongation. While the WT enzyme specifically produced GGPP, variants M87F and S88Y could only generate C15-farnesyl pyrophosphate (FPP), indicating that residues with large side chains obstruct product elongation. In contrast, replacement of M87 with the smaller Ala residue allowed the formation of the longer C25-geranylfarnesyl pyrophosphate (GFPP) product. Overall, our results provide new structural and functional information on the cyanobacterial CrtE enzyme that could lead to the development of improved cyanobacterial platforms for terpenoid production.