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首页> 外文期刊>Proceedings of the National Academy of Sciences of the United States of America >Structural insights into the pH-controlled targeting of plant cell-wall invertase by a specific inhibitor protein
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Structural insights into the pH-controlled targeting of plant cell-wall invertase by a specific inhibitor protein

机译：特定抑制剂蛋白对pH值控制植物细胞壁转化酶靶向作用的结构见解

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摘要

Invertases are highly regulated enzymes with essential functions in carbohydrate partitioning, sugar signaling, and plant development. Here we present the 2-6 A crystal structure of Arabidopsis cell-wall invertase 1 (INV1) in complex with a protein inhibitor (CIF, or cell-wall inhibitor of β-fructosidase) from tobacco. The structure identifies a small amino acid motif in CIF that directly targets the invertase active site. The activity of INV1 and its interaction with CIF are strictly pH-dependent with a maximum at about pH 4.5. At this pH, isothermal titration calorimetry reveals that CIF tightly binds its target with nanomolar affinity. CIF competes with sucrose (Suc) for the same binding site, suggesting that both the extracellular Suc concentration and the pH changes regulate association of the complex. A conserved glutamate residue in the complex interface was previously identified as an important quantitative trait locus affecting fruit quality, which implicates the invertase-inhibitor complex as a main regulator of carbon partitioning in plants. Comparison of the CIF/INV1 structure with the complex between the structurally CIF-related pectin methylesterase inhibitor (PMEI) and pectin meth-ylesterase indicates a common targeting mechanism in PMEI and CIF. However, CIF and PMEI use distinct surface areas to selectively inhibit very different enzymatic scaffolds.
机译：转化酶是高度调节的酶，在碳水化合物分配，糖信号传导和植物发育中具有基本功能。在这里，我们提出了拟南芥细胞壁转化酶1（INV1）的2-6 A晶体结构，与烟草中的蛋白质抑制剂（CIF或β-果糖苷酶的细胞壁抑制剂）复合。该结构可识别CIF中直接靶向转化酶活性位点的小氨基酸基序。 INV1的活性及其与CIF的相互作用严格依赖于pH，在约pH 4.5时达到最大值。在此pH下，等温滴定量热法显示CIF以纳摩尔亲和力紧密结合其靶标。 CIF与蔗糖（Suc）竞争相同的结合位点，表明细胞外Suc浓度和pH值变化均调节复合物的缔合。先前已将复合物界面中保守的谷氨酸残基鉴定为影响果实品质的重要定量性状基因座，这暗示了转化酶-抑制剂复合物是植物碳分配的主要调节剂。 CIF / INV1结构与CIF相关果胶甲基酯酶抑制剂（PMEI）和果胶甲基酯酶之间的复合物的比较表明，在PMEI和CIF中存在共同的靶向机制。但是，CIF和PMEI使用不同的表面积来选择性抑制非常不同的酶促支架。

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