Shedding light on lipid metabolism in Kinetoplastida: A phylogenetic analysis of phospholipase D protein homologs.

Unicellular flagellates that make up the class Kinetoplastida include multiple parasites responsible for public health concerns, including Trypanosoma brucei and T. cruzi (agents of African sleeping sickness and Chagas disease, respectively), and various Leishmania species, which cause leishmaniasis. These diseases are generally difficult to eradicate, with treatments often having lethal side effects and/or being effective only during the acute phase of the diseases, when most patients are still asymptomatic. Phospholipid signaling and metabolism are important in the different life stages of Trypanosoma, including playing a role in transitions between stages and in immune system evasion, thus, making the responsible enzymes into potential therapeutic targets. However, relatively little is understood about how the pathways function in these pathogens. Thus, in this study we examined evolutionary history of proteins from one such signaling pathway, namely phospholipase D (PLD) homologs. PLD is an enzyme responsible for synthesizing phosphatidic acid (PA) from membrane phospholipids. PA is not only utilized for phospholipid synthesis, but is also involved in many other signaling pathways, including biotic and abiotic stress response. 37 different representative Kinetoplastida genomes were used for an exhaustive search to identify putative PLD homologs. The genome of Bodo saltans was the only one of surveyed Kinetoplastida genomes that encoded a protein that clustered with plant PLDs. The representatives from other Kinetoplastida species clustered together in two different clades, thought to be homologous to the PLD superfamily, but with shared sequence similarity with cardiolipin synthases (CLS), and phosphatidylserine synthases (PSS). The protein structure predictions showed that most Kinetoplastida sequences resemble CLS and PSS, with the exception of 5 sequences from Bodo saltans that shared significant structural similarities with the PLD sequences, suggesting the loss of PLD-like sequences during the evolution of parasitism in kinetoplastids. On the other hand, diacylglycerol kinase (DGK) homologs were identified for all species examined in this study, indicating that DGK could be the only pathway for the synthesis of PA involved in lipid signaling in these organisms due to genome streamlining during transition to parasitic lifestyle. Our findings offer insights for development of potential therapeutic and/or intervention approaches, particularly those focused on using PA, PLD and/or DGK related pathways, against trypanosomiasis, leishmaniasis, and Chagas disease.