# Properties and predicted functions of large genes and proteins of apicomplexan parasites

## TL;DR

This paper explores the functions of unusually large proteins in apicomplexan parasites like Toxoplasma and Plasmodium, which may help them survive and interact with their hosts.

## Contribution

The study identifies potential functions of large proteins in apicomplexan parasites, including roles in immune evasion and host interaction.

## Key findings

- Large proteins in apicomplexan parasites contain domains linked to antigenic variation and erythrocyte invasion.
- Some large proteins are predicted to participate in metabolic pathways or host interactions.
- These large proteins are not strictly conserved and are expressed at low levels.

## Abstract

Evolutionary constraints greatly favor compact genomes that efficiently encode proteins. However, several eukaryotic organisms, including apicomplexan parasites such as Toxoplasma gondii, Plasmodium falciparum and Babesia duncani, the causative agents of toxoplasmosis, malaria and babesiosis, respectively, encode very large proteins, exceeding 20 times their average protein size. Although these large proteins represent <1% of the total protein pool and are generally expressed at low levels, their persistence throughout evolution raises important questions about their functions and possible evolutionary pressures to maintain them. In this study, we examined the trends in gene and protein size, function and expression patterns within seven apicomplexan pathogens. Our analysis revealed that certain large proteins in apicomplexan parasites harbor domains potentially important for functions such as antigenic variation, erythrocyte invasion and immune evasion. However, these domains are not limited to or strictly conserved within large proteins. While some of these proteins are predicted to engage in conventional metabolic pathways within these parasites, others fulfill specialized functions for pathogen–host interactions, nutrient acquisition and overall survival.

Graphical Abstract