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首页> 外文期刊>Biochemistry >Thermodynamic characterization of the protein-protein interaction in the heteromeric Bacillus subtilis pyridoxalphosphate synthase.
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Thermodynamic characterization of the protein-protein interaction in the heteromeric Bacillus subtilis pyridoxalphosphate synthase.

机译：枯草芽孢杆菌吡ido草磷酸合酶中的蛋白质-蛋白质相互作用的热力学表征。

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摘要

Two biosynthetic routes for the synthesis of pyridoxal 5'-phosphate (PLP), the biologically active compound of vitamin B6, have been characterized. The major pathway leads to direct formation of PLP from a pentasaccharide and a trisaccharide and is operative in plants, fungi, protozoa, and bacteria. This reaction is catalyzed by a single glutamine amidotransferase enzyme complex consisting of a pyridoxal synthase, termed Pdx1, and a glutaminase, termed Pdx2. In this complex, Pdx2 generates ammonia from L-glutamine and supplies it to Pdx1 for incorporation into PLP. The glutaminase activity of Pdx2 requires the presence of Pdx1 in a heteromeric complex, previously characterized by a crystallographic three-dimensional (3D) structure determination. Here, we give a thermodynamic description of complex formation of Bacillus subtilis PLP synthase in the absence or presence of L-glutamine. We show that L-glutamine directly affects the tightness of the protein complex, which exhibits dissociation constants of 6.9 and 0.3 microM in its absence and presence, respectively (at 25 degrees C). This result relates to the positioning of L-glutamine on the heterodimer interface as seen in the 3D structure. In an analysis of the temperature dependence of the enthalpy, negative heat capacity changes (deltaCp) agree with a protein interface governed by hydrophobic interactions. The measured heat capacity change is also a function of L-glutamine, with a negative deltaCp in the presence of L-glutamine and a more negative one in its absence. These findings suggest that L-glutamine not only affects the strength of complex formation but also determines the forces involved in complex formation, with regard to different relative contributions of hydrophobic and hydrophilic interactions.
机译：已经表征了两种合成维生素B6的生物活性化合物吡ido醛5'-磷酸（PLP）的生物合成途径。主要途径导致由五糖和三糖直接形成PLP，并且在植物，真菌，原生动物和细菌中起作用。该反应由单一的谷氨酰胺酰胺转移酶复合物催化，该复合物由吡ido醛合酶（称为Pdx1）和谷氨酰胺酶（称为Pdx2）组成。在这种复合物中，Pdx2从L-谷氨酰胺中产生氨，并将其供应给Pdx1，以掺入PLP中。 Pdx2的谷氨酰胺酶活性需要异聚复合物中存在Pdx1，该复合物先前通过晶体学三维（3D）结构确定来表征。在这里，我们给出了在不存在或存在L-谷氨酰胺的情况下枯草芽孢杆菌PLP合酶的复杂形成的热力学描述。我们显示，L-谷氨酰胺直接影响蛋白质复合物的紧密度，在不存在和存在时（分别在25摄氏度时）分别显示6.9和0.3 microM的解离常数。如在3D结构中所见，该结果与L-谷氨酰胺在异二聚体界面上的定位有关。在对焓的温度依赖性进行分析时，负热容变化（deltaCp）与受疏水相互作用控制的蛋白质界面一致。测得的热容量变化也是L-谷氨酰胺的函数，在存在L-谷氨酰胺的情况下，deltaCp为负，在不存在L-谷氨酰胺的情况下，ΔCp为负。这些发现表明，关于疏水和亲水相互作用的不同相对贡献，L-谷氨酰胺不仅影响复合物形成的强度，而且确定参与复合物形成的力。

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