USDA/ARS Children's Nutrition Research Center, Department of Pediatrics, Baylor College of Medicine, Houston, TX 77030, USA.
BioDiscovery Institute, University of North Texas, Denton, TX 76203, USA.
Int J Mol Sci. 2021 Mar 23;22(6):3266. doi: 10.3390/ijms22063266.
Considering the widespread occurrence of oxalate in nature and its broad impact on a host of organisms, it is surprising that so little is known about the turnover of this important acid. In plants, oxalate oxidase is the most well-studied enzyme capable of degrading oxalate, but not all plants possess this activity. Recently, acyl-activating enzyme 3 (AAE3), encoding an oxalyl-CoA synthetase, was identified in Arabidopsis. This enzyme has been proposed to catalyze the first step in an alternative pathway of oxalate degradation. Since this initial discovery, this enzyme and proposed pathway have been found to be important to other plants and yeast as well. In this study, we identify, in Arabidopsis, an oxalyl-CoA decarboxylase (AtOXC) that is capable of catalyzing the second step in this proposed pathway of oxalate catabolism. This enzyme breaks down oxalyl-CoA, the product of AtAAE3, into formyl-CoA and CO. AtOXC:GFP localization suggested that this enzyme functions within the cytosol of the cell. An knock-down mutant showed a reduction in the ability to degrade oxalate into CO. This reduction in AtOXC activity resulted in an increase in the accumulation of oxalate and the enzyme substrate, oxalyl-CoA. Size exclusion studies suggest that the enzyme functions as a dimer. Computer modeling of the AtOXC enzyme structure identified amino acids of predicted importance in co-factor binding and catalysis. Overall, these results suggest that AtOXC catalyzes the second step in this alternative pathway of oxalate catabolism.
考虑到草酸盐在自然界中的广泛存在及其对众多生物体的广泛影响，令人惊讶的是，人们对这种重要酸的周转率知之甚少。在植物中，草酸盐氧化酶是研究最多的能够降解草酸盐的酶，但并非所有植物都具有这种活性。最近，酰基辅酶 A 激活酶 3（AAE3），编码草酰辅酶 A 合成酶，在拟南芥中被鉴定出来。该酶被提议催化草酸盐降解的替代途径的第一步。自最初的发现以来，这种酶和提议的途径已被发现对其他植物和酵母也很重要。在这项研究中，我们在拟南芥中鉴定出一种能够催化草酸盐分解代谢替代途径第二步的草酰辅酶 A 脱羧酶（AtOXC）。该酶将草酰辅酶 A（AtAAE3 的产物）分解为甲酰辅酶 A 和 CO。AtOXC:GFP 定位表明该酶在细胞的细胞质中发挥作用。一个 敲低突变体显示出降低将草酸盐降解为 CO 的能力。AtOXC 活性的降低导致草酸盐和酶底物草酰辅酶 A 的积累增加。排阻层析研究表明该酶作为二聚体发挥作用。AtOXC 酶结构的计算机建模确定了预测在辅助因子结合和催化中重要的氨基酸。总体而言，这些结果表明 AtOXC 催化草酸盐分解代谢替代途径的第二步。
