Dissecting Leishmania infantum Energy Metabolism - A Systems Perspective

Abstract

Leishmania infantum, causative agent of visceral leishmaniasis in humans, illustrates a complex lifecycle pertaining to two extreme environments, namely, the gut of the sandfly vector and human macrophages. Leishmania is capable of dynamically adapting and tactically switching between these critically hostile situations. The possible metabolic routes ventured by the parasite to achieve this exceptional adaptation to its varying environments are still poorly understood. In this study, we present an extensively reconstructed energy metabolism network of Leishmania infantum as an attempt to identify certain strategic metabolic routes preferred by the parasite to optimize its survival in such dynamic environments. The reconstructed network consists of 142 genes encoding for enzymes performing 237 reactions distributed across five distinct model compartments. We annotated the subcellular locations of different enzymes and their reactions on the basis of strong literature evidence and sequence-based detection of cellular localization signal within a protein sequence. To explore the diverse features of parasite metabolism the metabolic network was implemented and analyzed as a constraint-based model. Using a systems-based approach, we also put forth an extensive set of lethal reaction knockouts; some of which were validated using published data on Leishmania species. Performing a robustness analysis, the model was rigorously validated and tested for the secretion of overflow metabolites specific to Leishmania under varying extracellular oxygen uptake rate. Further, the fate of important non-essential amino acids in L. infantum metabolism was investigated. Stage-specific scenarios of L. infantum energy metabolism were incorporated in the model and key metabolic differences were outlined. Analysis of the model revealed the essentiality of glucose uptake, succinate fermentation, glutamate biosynthesis and an active TCA cycle as driving forces for parasite energy metabolism and its optimal growth. Finally, through our in silico knockout analysis, we could identify possible therapeutic targets that provide experimentally testable hypotheses.

The Transcriptome ofLeishmania majorDevelopmental Stages in Their Natural Sand Fly Vector

“…This pattern was shared between the glucose transporters GT1, GT2, and GT3 (LmjF.36.6300, LmjF.36.6290, and LmjF.36.6280, respectively) and the amino acid transporter AAP24 (LmjF.10.0720, LmjF.10.0715, and LmjF.10.0720, also known as AAT20 1 to 3). This transporter is specific for “nonessential” amino acids, such as proline and alanine, that are known to serve as carbon sources in Leishmania (4, 30–33). Moreover, the transporter has a role in maintaining the homeostasis of amino acids in the free amino acid pool, in which proline, alanine, and glutamate are the most abundant constituents (32, 34).…”

“…Other glycolysis enzymes, such as the phosphoglucose isomerase (PGI) (LmjF.12.0530) and the putative hexokinase (LmjF.21.0240), were significantly upregulated in PP and NP compared to AM, with no significant difference between MP and AM (modules 15 and 145, respectively), suggesting that glycolysis is downregulated at the MP stage, possibly as a preadaptation to the intraphagosomal environment, where energy is produced by other carbon sources, such as fatty acids and amino acids. A main pathway of amino acid utilization in Leishmania is through the metabolism of glutamate (32, 33). Glutamate is metabolized by glutamate dehydrogenase (GDH), which converts glutamate to α-ketoglutarate to enter the TCA cycle and vice versa.…”

System pharmacogenomics application in infectious diseases

“…It was observed that any reduction in the enzyme activity and or reaction flux leads to reduction in the survival rate of the parasite, suggesting that both these enzymes could be good druggable targets. In addition to the in silico predicted flux profiles of L. major metabolism, the importance of evolutionary rates of these metabolic enzymes has also been highlighted [45]. On similar lines, in a study done by Chavli et al, evaluation of fluxes through the F 0 F 1 -ATP synthase reaction resulted in the construction of iAC560 MODEL.…”

The Experimental Proteome of Leishmania infantum promastigote and Its Usefulness for Improving Gene Annotations

“…By the KEGG database resource (http://www.genome.jp/kegg/) accessed via DAVID package, a total of 578 (27.6%) of the detected proteins could be classified into pathways representing classical cellular processes. In particular, 236 proteins were identified as metabolic enzymes; 31% of these enzymes belong to glycolysis (Tables 1 and 2), tricarboxylic acid (TCA) cycle and pentose phosphate cycle (Supplementary file, Table S4), three metabolic pathways playing essential maintenance functions in the cell [47]. Remarkably, the complete set of 29 enzymes that make up the TCA cycle were identified in the promastigote proteome ( Figure 3).…”