Abstract
Apicomplexan parasites possess a unique cortical cytoskeleton structure composed of intermediate filaments. Its building blocks are provided by a conserved family of proteins named alveolins. The core alveolin structure is made up of tandem repeat sequences, thought to be responsible for the filamentous properties of these proteins. A subset of alveolins also possess conserved motifs composed of three closely spaced cysteine residues situated near the ends of the polypeptides. The roles of these cysteine motifs and their contribution to alveolin function remains poorly understood. The sporozoite-expressed IMC1a is unique within the Plasmodium alveolin family in having conserved cysteine motifs at both termini. Using transgenic Plasmodium berghei parasites, we show in this structure-function analysis that mutagenesis of the amino- or carboxy-terminal cysteine motif causes marked reductions in IMC1a protein levels in the parasite, which are accompanied by partial losses of sporozoite shape and infectivity. Our findings give new insight into alveolin function, identifying a dose-dependent effect of alveolin depletion on sporozoite size and infectivity, and vital roles of the terminal cysteine motifs in maintaining alveolin stability in the parasite.
Highlights
Plasmodium species, the causative agents of malaria, have a complex life cycle in vertebrate host and mosquito vector
In this study we have employed red fluorescent protein tagging in transgenic P. berghei parasites to study the function of the terminal cysteine residues of the alveolin IMC1a
Assuming that IMC1a expression was not affected by the cysteine mutations, this suggests that the reductions in IMC1a levels occurred soon after translation and possibly before IMC1a recruitment to the pellicle
Summary
Plasmodium species, the causative agents of malaria, have a complex life cycle in vertebrate host and mosquito vector. The zoites of Plasmodium, as well as those of related apicomplexan parasites, possess an unusual cortical structure termed the pellicle. In the genus Plasmodium, 13 conserved and syntenic alveolin family members have been identified that are differentially expressed among the three different zoites stages of malaria parasites [7,8]. It has been shown in the rodent malaria species P. berghei that disruption of alveolins gives rise to morphological aberrations that are accompanied by reduced tensile strength of the zoite stages in which they are found [5,8,9,10,11]. Plasmodium alveolins have roles in parasite gliding motility [5,9,10,11] most likely by tethering glideosome associated proteins that reside in the IMC
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