Centro de Estudios Fotosinteticos y Bioquimicos (CEFOBI-CONICET), Facultad de Ciencias Bioquímicas y Farmacéuticas, University of Rosario, Rosario, Argentina.
Plant Molecular Physiology and Biotechnology Group, Institute of Developmental and Molecular Biology of Plants, Heinrich Heine University Düsseldorf, Düsseldorf, Germany.
Nat Plants. 2019 Jul;5(7):755-765. doi: 10.1038/s41477-019-0451-7. Epub 2019 Jun 24.
In C grasses of agronomical interest, malate shuttled into the bundle sheath cells is decarboxylated mainly by nicotinamide adenine dinucleotide phosphate (NADP)-malic enzyme (C-NADP-ME). The activity of C-NADP-ME was optimized by natural selection to efficiently deliver CO to Rubisco. During its evolution from a plastidic non-photosynthetic NADP-ME, C-NADP-ME acquired increased catalytic efficiency, tetrameric structure and pH-dependent inhibition by its substrate malate. Here, we identified specific amino acids important for these C adaptions based on strict differential conservation of amino acids, combined with solving the crystal structures of maize and sorghum C-NADP-ME. Site-directed mutagenesis and structural analyses show that Q503, L544 and E339 are involved in catalytic efficiency; E339 confers pH-dependent regulation by malate, F140 is critical for the stabilization of the oligomeric structure and the N-terminal region is involved in tetramerization. Together, the identified molecular adaptations form the basis for the efficient catalysis and regulation of one of the central biochemical steps in C metabolism.
在农艺学上有重要意义的 C4 类禾本科植物中，通过苹果酸穿梭作用进入维管束鞘细胞的苹果酸主要由烟酰胺腺嘌呤二核苷酸磷酸（NADP）-苹果酸酶（C-NADP-ME）脱羧。C-NADP-ME 的活性经过自然选择得到优化，能够有效地将 CO 输送给 Rubisco。在从质体非光合型 NADP-ME 进化而来的过程中，C-NADP-ME 获得了更高的催化效率、四聚体结构以及对其底物苹果酸的 pH 依赖性抑制。基于严格的氨基酸差异保守性，结合解析出的玉米和高粱 C-NADP-ME 的晶体结构，我们鉴定出了这些 C 适应过程中重要的特定氨基酸。定点突变和结构分析表明，Q503、L544 和 E339 参与了催化效率；E339 通过苹果酸赋予 pH 依赖性调节，F140 对于寡聚体结构的稳定至关重要，而 N 端区域则参与了四聚体化。综上所述，所鉴定出的分子适应为 C 代谢中一个核心生化步骤的高效催化和调节提供了基础。
