Plasmodium Repetome: A mysterious space with a wealth of information

Eukaryotic proteomes harbour repetitive stretches of amino acids that may play critical roles in the biology of that organism. While several tandem repeats (TR) are known to contribute to protein structure and function, information about the vast majority of repeat regions remains obscure. In this article, we have analysed the repeat content of different Plasmodium species and found the leading human malaria-causing P. falciparum (Pf) and P. vivax to be exceptionally rich in TR regions (>40% TR containing proteins). Detailed analysis of Pf ‘repetome’ showed this intracellular parasite to carry longer TRs,several of which were present in exported proteins important for parasite survival and immune evasion. The repeat regions of Pf were enriched in acidic amino acids and asparagine (Asn), where Asn was more abundant in short and intermediate TRs, suggesting an evolutionary bias influenced by replication slippage and positive selection. Gene ontology analysis of TR containing Pf proteins helped us to understand their cellular localization along with the molecular and biological processes they are involved in. The Pf variable surface antigen families with roles in important pathogenic processes like cytoadherence, immune evasion etc. had low repeat content present within seroreactive peptides. Three-dimensional structure predictions of TR regions revealed several repeats to adopt ordered super-secondary conformations that are known to facilitate intermolecular interactions. Overall, this is a comprehensive study attempting to gain insights on the importance of TRs in malaria parasite biology and suggests a novel route to understanding protein function through the characterization of repeat content.