Chaperoning of asparagine repeat-containing proteins in Plasmodium falciparum
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REVIEW ARTICLE
Chaperoning of asparagine repeat-containing proteins in Plasmodium falciparum Thavamani Rajapandi1
Received: 28 May 2020 / Accepted: 18 July 2020 Ó Indian Society for Parasitology 2020
Abstract Plasmodium falciparum has the most adenine (A)- and thymine (T)-rich genome known to date, and 24–30% of the P. falciparum proteome contains asparagine (N) and glutamine (Q) residues. In general, asparagine repeats in proteins increase the propensity for aggregation, especially at elevated temperatures, which occur routinely in P. falciparum parasites during exoerythrocytic and erythrocytic developmental stages in a vertebrate host. The P. falciparum exported chaperone machinery is comprised of an exported PfHsp70-x protein and its co-chaperone PfHsp40-x1 in the host erythrocyte compartment, and PfHsp70-z and its co-chaperones in the parasite cytoplasm have been identified. In vitro assays reveal that these chaperone partners function in refolding of asparagine-rich polypeptides. The identification and chaperoning of exported poly-asparagine-containing proteins, and the biological roles and the protection mechanisms of P. falciparum during febrile conditions by the exported chaperone machinery are discussed. Keywords Plasmodium falciparum Chaperone Asparagine repeat
& Thavamani Rajapandi [email protected] 1
Department of Natural Sciences, Science and Technology Center, Coppin State University, 2500 West North Avenue, Baltimore, MD 21216-3698, USA
Introduction Malaria, primarily Plasmodium falciparum malaria, which is the deadliest, is centered around sub-Saharan African countries and most of the tropical regions in Asia. According to the 2019 World Malaria Report, malaria caused approximately 405,000 deaths in 2018 and the number of malaria cases was estimated to be 228 million. The genome sequence information of several P. falciparum lines (www.PlasmoDB.Org) reveals the presence of very high (A ? T)-rich nucleotide sequence (Gardner et al. 2002). This review analyzes the significance of (A ? T)rich P. falciparum genome, poly-asparagine (Poly-N)-rich proteome, chaperoning, export of asparagine- and glutamine-rich proteins, and the physiological significance of this unique proteome in the survival and pathogenicity of P. falciparum.
(A 1 T)-richness and the expansion of polyN repeat-containing proteins in P. falciparum The P. falciparum genome, which is comprised of 80.6% (A ? T) nucleotides, encodes approximately 5,300 proteins, with [ 60% of these proteins being hypothetical proteins. A comparative proteome analysis of seven different organisms identified that approximately 35% of P. falciparum proteins have repeats of amino acids significantly higher than in other fully sequenced eukaryotes (Singh et al. 2004). These amino acid repeats are dominated by asparagine (abbreviation: three-letter: Asn, Oneletter: N, codons: AAU, AAC, GAU and GAC) which are selected over lysine (Lys, K, codons: AAA or AAG) despite equivalent A-T nucleotide content. In P. falciparum, 24–30% of the proteins are poly-Gl
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