Detarsio Enrique, Alvarez Clarisa E, Saigo Mariana, Andreo Carlos S, Drincovich María F
Centro de Estudios Fotosintéticos y Bioquímicos (CEFOBI), Universidad Nacional de Rosario, Suipacha 531, Rosario, Argentina.
J Biol Chem. 2007 Mar 2;282(9):6053-60. doi: 10.1074/jbc.M609436200. Epub 2006 Dec 6.
C(4) photosynthetic NADP-malic enzyme (ME) has evolved from non-C(4) isoforms and gained unique kinetic and structural properties during this process. To identify the domains responsible for the structural and kinetic differences between maize C(4) and non-C(4)-NADP-ME several chimeras between these isoforms were constructed and analyzed. By using this approach, we found that the region flanked by amino acid residues 102 and 247 is critical for the tetrameric state of C(4)-NADP-ME. In this way, the oligomerization strategy of these NADP-ME isoforms differs markedly from the one that present non-plant NADP-ME with known crystal structures. On the other hand, the region from residue 248 to the C-terminal end of the C(4) isoform is involved in the inhibition by high malate concentrations at pH 7.0. The inhibition pattern of the C(4)-NADP-ME and some of the chimeras suggested an allosteric site responsible for such behavior. This pH-dependent inhibition could be important for regulation of the C(4) isoform in vivo, with the enzyme presenting maximum activity while photosynthesis is in progress.
C4光合型NADP - 苹果酸酶（ME）由非C4同工型进化而来，并在此过程中获得了独特的动力学和结构特性。为了确定玉米C4和非C4 - NADP - ME之间结构和动力学差异的负责结构域，构建并分析了这些同工型之间的几种嵌合体。通过这种方法，我们发现由氨基酸残基102和247侧翼的区域对于C4 - NADP - ME的四聚体状态至关重要。这样，这些NADP - ME同工型的寡聚化策略与具有已知晶体结构的非植物NADP - ME明显不同。另一方面，从残基248到C4同工型C末端的区域参与了在pH 7.0时高苹果酸浓度的抑制作用。C4 - NADP - ME和一些嵌合体的抑制模式表明存在一个负责这种行为的变构位点。这种pH依赖性抑制对于体内C4同工型的调节可能很重要，因为该酶在光合作用进行时呈现最大活性。
