Department of Microbiology and Immunology, Loyola University Chicago Stritch School of Medicine, Maywood, Illinois, USA.
Department of Microbiology and Immunology, Loyola University Chicago Stritch School of Medicine, Maywood, Illinois, USA
J Bacteriol. 2019 Oct 21;201(22). doi: 10.1128/JB.00446-19. Print 2019 Nov 15.
competes for myriad essential nutrients during host infection. One of these nutrients is the organosulfur compound lipoic acid, a cofactor required for the activity of several metabolic enzyme complexes. In , these include the E2 subunits of three α-ketoacid dehydrogenases and two H proteins, GcvH of the glycine cleavage system and its paralog, GcvH-L. We previously determined that the amidotransferase LipL is required for lipoylation of the E2 subunits of pyruvate dehydrogenase (PDH) and branched-chain 2-oxoacid dehydrogenase (BCODH) complexes. The results from this study, coupled with those from , suggested that LipL catalyzes lipoyl transfer from H proteins to E2 subunits. However, to date, the range of LipL targets, the extent of LipL-dependent lipoic acid shuttling between lipoyl domain-containing proteins, and the importance of lipoyl relay in pathogenesis remain unknown. Here, we demonstrate that LipL uses both lipoyl-H proteins as the substrates for lipoyl transfer to all E2 subunits. Moreover, LipL facilitates lipoyl relay between E2 subunits and between H proteins, a property that potentially constitutes an adaptive response to nutrient scarcity in the host, as LipL is required for virulence during infection. Together, these observations support a role for LipL in facilitating flexible lipoyl relay between proteins and highlight the complexity of protein lipoylation in Protein lipoylation is a posttranslational modification that is evolutionarily conserved from bacteria to humans. Lipoic acid modifications are found on five proteins in , four of which are components of major metabolic enzymes. In some bacteria, the amidotransferase LipL is critical for the attachment of lipoic acid to these proteins, and yet it is unclear to what extent LipL facilitates the transfer of this cofactor. We find that LipL flexibly shuttles lipoic acid among metabolic enzyme subunits, alluding to a dynamic redistribution mechanism within the bacterial cell. This discovery exemplifies a potential means by which bacteria optimize the use of scarce nutrients when resources are limited.
在宿主感染过程中，它会与其他病原体竞争无数必需的营养物质。其中一种营养物质是有机硫化合物硫辛酸，它是几种代谢酶复合物活性所必需的辅助因子。在 中，这些包括三种α-酮酸脱氢酶的 E2 亚基和两种 H 蛋白，即甘氨酸裂解系统的 GcvH 及其同工酶 GcvH-L。我们之前确定，酰胺转移酶 LipL 是丙酮酸脱氢酶（PDH）和支链 2-氧酸脱氢酶（BCODH）复合物的 E2 亚基脂酰化所必需的。这项研究的结果，加上之前的研究结果，表明 LipL 催化 H 蛋白向 E2 亚基的脂酰转移。然而，迄今为止，LipL 的靶标范围、脂酰化转移酶 LipL 依赖性脂酰硫辛酸在含脂酰结构域蛋白之间的转移程度，以及脂酰化转移在发病机制中的重要性仍不清楚。在这里，我们证明 LipL 既可以作为底物将脂酰基转移到所有 E2 亚基上，也可以作为 H 蛋白的底物将脂酰基转移到所有 E2 亚基上。此外，LipL 促进 E2 亚基之间以及 H 蛋白之间的脂酰化转移，这一特性可能构成了对宿主营养物质匮乏的适应性反应，因为 LipL 是感染期间毒力所必需的。综上所述，这些观察结果支持 LipL 在促进蛋白质之间灵活的脂酰化转移中的作用，并强调了 中蛋白质脂酰化的复杂性。
蛋白质脂酰化是一种从细菌到人类都具有进化保守性的翻译后修饰。在 中，有 5 种蛋白质上发现了脂酰化修饰，其中 4 种是主要代谢酶的组成部分。在一些细菌中，酰胺转移酶 LipL 对这些蛋白质上脂酰酸的附着至关重要，但尚不清楚 LipL 在多大程度上促进了这种辅助因子的转移。我们发现 LipL 可以灵活地在代谢酶亚基之间穿梭脂酰硫辛酸，这暗示了细菌细胞内存在一种动态的再分配机制。这一发现为细菌在资源有限时优化利用稀缺营养物质提供了一种潜在的手段。
