Laboratory of Molecular Pathogenesis, Department of Biochemistry, School of Life Science, University of Hyderabad, Hyderabad 500046, India.
Inflammation Biology and Cell Signaling Laboratory, National Institute of Pathology, New Delhi 110029, India; Jamia Hamdard Institute of Molecular Medicine, Jamia Hamdard, Hamdard Nagar, New Delhi 110062, India.
Int J Med Microbiol. 2022 Jan;312(1):151544. doi: 10.1016/j.ijmm.2021.151544. Epub 2021 Dec 7.
Mycobacterium tuberculosis (M. tuberculosis) encodes an essential enzyme acetyl ornithine aminotransferase ArgD (Rv1655) of arginine biosynthetic pathway which plays crucial role in M. tuberculosis growth and survival. ArgD catalyzes the reversible conversion of N-acetylornithine and 2 oxoglutarate into glutamate-5-semialdehyde and L-glutamate. It also possesses succinyl diaminopimelate aminotransferase activity and can thus carry out the corresponding step in lysine biosynthesis. These essential roles played by ArgD in amino acid biosynthetic pathways highlight it as an important metabolic chokepoint thus an important drug target. We showed that M. tuberculosis ArgD rescues the growth of ΔargD E. coli grown in minimal media validating its functional importance. Phylogenetic analysis of M. tuberculosis ArgD showed homology with proteins in gram positive bacteria, pathogenic and non-pathogenic mycobacteria suggesting the essentiality of this protein. ArgD is a secretory protein that could be utilized by M. tuberculosis to modulate host innate immunity as its moonlighting function. In-silico analysis predicted it to be a highly antigenic protein. The recombinant ArgD protein when exposed to macrophage cells induced enhanced production of pro-inflammatory cytokines TNF, IL6 and IL12 in a dose dependent manner. ArgD also induced the increased production of innate immune effector molecule NOS2 and NO in macrophages. We also demonstrated ArgD mediated activation of the canonical NFkB pathway. Notably, we also show that ArgD is a specific TLR4 agonist involved in the activation of pro-inflammatory signaling for sustained production of effector cytokines. Intriguingly, ArgD protein treatment activated macrophages to acquire the M1 phenotype through the increased surface expression of MHCII and costimulatory molecules CD80 and CD86. ArgD induced robust B-cell response in immunized mice, validating its antigenicity potential as predicted by the in-silico analysis. These properties of M. tuberculosis ArgD signify its functional plasticity that could be exploited as a possible drug target to combat tuberculosis.
结核分枝杆菌（M. tuberculosis）编码精氨酸生物合成途径中必需的酶乙酰鸟氨酸氨基转移酶 ArgD（Rv1655），该酶在结核分枝杆菌的生长和存活中起着至关重要的作用。ArgD 催化 N-乙酰鸟氨酸和 2-氧代戊二酸可逆转化为谷氨酸-5-半醛和 L-谷氨酸。它还具有琥珀酰二氨基庚二酸氨基转移酶活性，因此可以进行赖氨酸生物合成中的相应步骤。ArgD 在氨基酸生物合成途径中发挥的这些重要作用使其成为一个重要的代谢关键酶，因此也是一个重要的药物靶标。我们表明，结核分枝杆菌 ArgD 挽救了在最小培养基中生长的ΔargD大肠杆菌的生长，验证了其功能的重要性。结核分枝杆菌 ArgD 的系统发育分析显示与革兰氏阳性菌、致病性和非致病性分枝杆菌的蛋白质同源，表明该蛋白的重要性。ArgD 是一种分泌蛋白，可能被结核分枝杆菌用来调节宿主先天免疫，因为它具有兼职功能。计算机分析预测它是一种高度抗原性蛋白。重组 ArgD 蛋白暴露于巨噬细胞时，可剂量依赖性地诱导促炎细胞因子 TNF、IL6 和 IL12 的产生增加。ArgD 还诱导巨噬细胞中先天免疫效应分子 NOS2 和 NO 的产生增加。我们还证明 ArgD 介导了经典 NFkB 途径的激活。值得注意的是，我们还表明 ArgD 是一种特定的 TLR4 激动剂，参与了促炎信号的激活，以持续产生效应细胞因子。有趣的是，ArgD 蛋白处理激活的巨噬细胞通过 MHCII 和共刺激分子 CD80 和 CD86 的表面表达增加获得 M1 表型。ArgD 在免疫小鼠中诱导强烈的 B 细胞反应，验证了其作为预测抗原性的潜力。这些结核分枝杆菌 ArgD 的特性表明其功能可塑性，可作为一种可能的药物靶标用于治疗结核病。
