Abstract
Lipoic acid (LA) is an essential cofactor of α-keto acid dehydrogenase complexes (KADHs) and the glycine cleavage system. In Plasmodium, LA is attached to the KADHs by organelle-specific lipoylation pathways. Biosynthesis of LA exclusively occurs in the apicoplast, comprising octanoyl-[acyl carrier protein]: protein N-octanoyltransferase (LipB) and LA synthase. Salvage of LA is mitochondrial and scavenged LA is ligated to the KADHs by LA protein ligase 1 (LplA1). Both pathways are entirely independent, suggesting that both are likely to be essential for parasite survival. However, disruption of the LipB gene did not negatively affect parasite growth despite a drastic loss of LA (>90%). Surprisingly, the sole, apicoplast-located pyruvate dehydrogenase still showed lipoylation, suggesting that an alternative lipoylation pathway exists in this organelle. We provide evidence that this residual lipoylation is attributable to the dual targeted, functional lipoate protein ligase 2 (LplA2). Localisation studies show that LplA2 is present in both mitochondrion and apicoplast suggesting redundancy between the lipoic acid protein ligases in the erythrocytic stages of P. falciparum.
Highlights
Lipoic acid (6,8-thioctic acid; LA) is an essential cofactor that is covalently attached to the transacylase subunit (E2subunit) of a-keto acid dehydrogenase complexes (KADHs), namely pyruvate dehydrogenase (PDH), a-keto glutarate dehydrogenase (KGDH), and branched chain a-keto acid dehydrogenase (BCDH) as well as the H-protein of the glycine cleavage system (GCS) [1,2]
In this study we show that the apicoplast located lipoic acid protein ligase, octanoyl-[acyl carrier protein]: protein N-octanoyltransferase (LipB), is not essential for parasite survival by disrupting the LipB gene locus
Despite a drastic loss of total lipoic acid, the parasites progress through their intraerythrocytic development unperturbed the apicoplast-located PDH shows a reduced level of lipoylation
Summary
Lipoic acid (6,8-thioctic acid; LA) is an essential cofactor that is covalently attached to the transacylase subunit (E2subunit) of a-keto acid dehydrogenase complexes (KADHs), namely pyruvate dehydrogenase (PDH), a-keto glutarate dehydrogenase (KGDH), and branched chain a-keto acid dehydrogenase (BCDH) as well as the H-protein of the glycine cleavage system (GCS) [1,2]. In eukaryotes, these multienzyme complexes are generally found in the mitochondrion. Bacterial-type LA protein ligases (LplA) catalyse the activation and transfer of LA in a single enzymatic step [6]
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