Van Kerckhoven Sonia H, de la Torre Fernando N, Cañas Rafael A, Avila Concepción, Cantón Francisco R, Cánovas Francisco M
Departamento de Biología Molecular y Bioquímica, Facultad de Ciencias, Universidad de MálagaMálaga, Spain.
Front Plant Sci. 2017 Jun 23;8:1075. doi: 10.3389/fpls.2017.01075. eCollection 2017.
Asparaginases (ASPG, EC 3.5.1.1) catalyze the hydrolysis of the amide group of L-asparagine producing L-aspartate and ammonium. Three ASPG, PpASPG1, PpASPG2, and PpASPG3, have been identified in the transcriptome of maritime pine ( Ait.) that were transiently expressed in by agroinfection. The three recombinant proteins were processed to active enzymes and it was found that all mature forms exhibited double activity asparaginase/isoaspartyl dipeptidase but only PpASPG1 was able to catalyze efficiently L-asparagine hydrolysis. PpASPG1 contains a variable region of 77 amino acids that is critical for proteolytic processing of the precursor and is retained in the mature enzyme. Furthermore, the functional analysis of deletion mutants demonstrated that this protein fragment is required for specific recognition of the substrate and favors enzyme stability. Potassium has a limited effect on the activation of maritime pine ASPG what is consistent with the lack of a critical residue essential for interaction of cation. Taken together, the results presented here highlight the specific features of ASPG from conifers when compared to the enzymes from angiosperms.
天冬酰胺酶（ASPG，EC 3.5.1.1）催化L-天冬酰胺的酰胺基团水解，生成L-天冬氨酸和铵。在海岸松（Ait.）的转录组中已鉴定出三种ASPG，即PpASPG1、PpASPG2和PpASPG3，它们通过农杆菌介导的瞬时表达在[具体实验对象]中表达。这三种重组蛋白被加工成活性酶，并且发现所有成熟形式均表现出天冬酰胺酶/异天冬氨酰二肽酶双重活性，但只有PpASPG1能够高效催化L-天冬酰胺水解。PpASPG1包含一个77个氨基酸的可变区，该区域对于前体的蛋白水解加工至关重要，并保留在成熟酶中。此外，缺失突变体的功能分析表明，该蛋白片段是底物特异性识别所必需的，并且有利于酶的稳定性。钾对海岸松ASPG的激活作用有限，这与缺乏阳离子相互作用所必需的关键残基一致。综上所述，与被子植物的酶相比，本文呈现的结果突出了针叶树ASPG的特异性特征。
