National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, 100101, People's Republic of China.
Department of Molecular and Cellular Physiology, 279 Campus Drive, Stanford University School of Medicine, Stanford, CA, 94305, USA.
Nat Commun. 2020 Mar 23;11(1):1525. doi: 10.1038/s41467-020-15268-y.
Long-chain alk(a/e)nes represent the major constituents of conventional transportation fuels. Biosynthesis of alkanes is ubiquitous in many kinds of organisms. Cyanobacteria possess two enzymes, acyl-acyl carrier protein (acyl-ACP) reductase (AAR) and aldehyde-deformylating oxygenase (ADO), which function in a two-step alkane biosynthesis pathway. These two enzymes act in series and possibly form a complex that efficiently converts long chain fatty acyl-ACP/fatty acyl-CoA into hydrocarbon. While the structure of ADO has been previously described, structures of both AAR and AAR-ADO complex have not been solved, preventing deeper understanding of this pathway. Here, we report a ligand-free AAR structure, and three AAR-ADO complex structures in which AARs bind various ligands. Our results reveal the binding pattern of AAR with its substrate/cofactor, and suggest a potential aldehyde-transferring channel from AAR to ADO. Based on our structural and biochemical data, we proposed a model for the complete catalytic cycle of AAR.
长链烷烃（a/e）是传统运输燃料的主要成分。烷烃的生物合成在许多种生物中普遍存在。蓝细菌拥有两种酶，酰基辅酶 A（酰基-ACP）还原酶（AAR）和醛脱甲酰基氧化酶（ADO），它们在两步烷烃生物合成途径中发挥作用。这两种酶串联作用，可能形成一个复合物，有效地将长链脂肪酸-ACP/脂肪酸-CoA 转化为烃。虽然 ADO 的结构以前已经描述过，但 AAR 和 AAR-ADO 复合物的结构尚未解决，这阻碍了对该途径的更深入理解。在这里，我们报告了一个无配体的 AAR 结构，以及三个 AAR-ADO 复合物结构，其中 AAR 结合了各种配体。我们的结果揭示了 AAR 与其底物/辅因子的结合模式，并提出了 AAR 向 ADO 转移醛的潜在通道。基于我们的结构和生化数据，我们提出了 AAR 完整催化循环的模型。
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