Housekeeping and other metabolic functions of the Plasmodium plastid

The malaria parasite carries a plastid called the apicoplast that has been the subject of intense study in the last 15 years. Having originated from red-algal plastids, the apicoplast has lost its ability to photosynthesize, but carries out other essential functions such as type-II fatty acid synthesis, biosynthesis of haem and isoprenoid synthesis; the DOXP pathway for isoprenoid synthesis has recently been demonstrated to be the only pathway critical for parasite survival in the erythrocytic stage. The apicoplast also has a functional Suf system for assembly of (Fe–S) complexes on target proteins. The organelle has a 35 kb, double-stranded DNA genome that encodes a set of RNAs and proteins, the latter being translated from organellar mRNA by an active translation machinery, a major component of which is encoded by the nucleus. This article reviews current knowledge of housekeeping functions of the Plasmodium apicoplast and its (Fe–S) assembly system and discusses these components as sites for drug intervention against malaria

Translation in organelles of apicomplexan parasites

The protein translation machineries of the apicoplast and mitochondrion–the two actively translating organelles of apicomplexan parasites–have potential sites for drug intervention against diseases caused by these organisms. Work in the past few years, particularly on Plasmodium falciparum and Toxoplasma gondii, has shown that a reduced machinery of enzymes and factors is sufficient for organellar translation, which is also supported by components shared with the cytosolic translation system. This interplay between eukaryotic and prokaryotic-like components for mRNA translation in organelles is reviewed here. We also discuss functional and structural aspects of factors mediating initiation, elongation, and termination of polypeptides, and recycling of the reduced ribosomes of the apicoplast and mitochondrion

MicroRNA, Proteins, and Metabolites as Novel Biomarkers for Prediabetes, Diabetes, and Related Complications

Type 2 diabetes mellitus (T2DM) is no more a lifestyle disease of developed countries. It has emerged as a major health problem worldwide including developing countries. However, how diabetes could be detected at an early stage (prediabetes) to prevent the progression of disease is still unclear. Currently used biomarkers like glycated hemoglobin and assessment of blood glucose level have their own limitations. These classical markers can be detected when the disease is already established. Prognosis of disease at early stages and prediction of population at a higher risk require identification of specific markers that are sensitive enough to be detected at early stages of disease. Biomarkers which could predict the risk of disease in people will be useful for developing preventive/proactive therapies to those individuals who are at a higher risk of developing the disease. Recent studies suggested that the expression of biomolecules including microRNAs, proteins, and metabolites specifically change during the progression of T2DM and related complications, suggestive of disease pathology. Owing to their omnipresence in body fluids and their association with onset, progression, and pathogenesis of T2DM, these biomolecules can be potential biomarker for prognosis, diagnosis, and management of disease. In this article, we summarize biomolecules that could be potential biomarkers and their signature changes associated with T2DM and related complications during disease pathogenesis

Polypeptide release factors and stop codon recognition in the apicoplast and mitochondrion of Plasmodium falciparum

Summary: Correct termination of protein synthesis would be a critical step in translation of organellar open reading frames (ORFs) of the apicoplast and mitochondrion of the malaria parasite. We identify release factors (RFs) responsible for recognition of the UAA and UGA stop-codons of apicoplast ORFs and the sole UAA stop-codon that terminates translation from the three mitochondrial ORFs. A single nuclear-encoded canonical RF2, PfRF2Api, localizes to the apicoplast. It has a conserved tripeptide motif (SPF) for stop-codon recognition and is sufficient for peptidyl-tRNA hydrolysis (PTH) from both UAA and UGA. Two RF family proteins are targeted to the parasite mitochondrion; a canonical RF1, PfRF1Mit, with a variant codon-recognition motif (PxN instead of the conserved RF1 PxT) is the major peptidyl-hydrolase with specific recognition of the UAA codon relevant to mitochondrial ORFs. Mutation of the N residue of the PfRF1Mit PxN motif and two other conserved residues of the codon recognition domain lowers PTH activity from pre-termination ribosomes indicating their role in codon-recognition. The second RF imported by the mitochondrion is the non-canonical PfICT1 that functions as a dimer and mediates codon nonspecific peptide release. Our results help delineate a critical step in organellar translation in Plasmodium, which is an important target for anti-malarials

The effect of fusidic acid on Plasmodium falciparum elongation factor G (EF-G)

Inhibition of growth of the malaria parasite Plasmodium falciparum by known translation-inhibitory antibiotics has generated interest in understanding their action on the translation apparatus of the two genome containing organelles of the malaria parasite: the mitochondrion and the relic plastid (apicoplast). We report GTPase activity of recombinant EF-G proteins that are targeted to the organelles and further use these to test the effect of the EF-G inhibitor fusidic acid (FA) on the factor–ribosome interface. Our results monitoring locking of EF-G·GDP onto surrogate Escherichia coli ribosomes as well as multi-turnover GTP hydrolysis by the factor indicate that FA has a greater effect on apicoplast EF-G compared to the mitochondrial counterpart. Deletion of a three amino acid (GVG) sequence in the switch I loop that is conserved in proteins of the mitochondrial EF-G1 family and the Plasmodium mitochondrial factor, but is absent in apicoplast EF-G, demonstrated that this motif contributes to differential inhibition of the two EF-Gs by FA. Additionally, the drug thiostrepton, that is known to target the apicoplast and proteasome, enhanced retention of only mitochondrial EF-G on ribosomes providing support for the reported effect of the drug on parasite mitochondrial translation