The relationship between protein domains and homopeptides in the Plasmodium falciparum proteome

Abstract

The proteome of the malaria parasite Plasmodium falciparum is notable for the pervasive occurrence of homopeptides or low-complexity regions (i.e., regions that are made from a small subset of amino-acid residue types). The most prevalent of these are made from residues encoded by adenine/thymidine (AT)-rich codons, in particular asparagine. We examined homopeptide occurrences within protein domains in P. falciparum. Homopeptide enrichments occur for hydrophobic (e.g., valine), or small residues (alanine or glycine) in short spans (<5 residues), but these enrichments disappear for longer lengths. We observe that short asparagine homopeptides (<10 residues long) have a dramatic relative depletion inside protein domains, indicating some selective constraint to keep them from forming. We surmise that this is possibly linked to co-translational protein folding, although there are specific protein domains that are enriched in longer asparagine homopeptides (≥10 residues) indicating a functional linkage for specific poly-asparagine tracts. Top gene ontology functional category enrichments for homopeptides associated with diverse protein domains include “vesicle-mediated transport”, and “DNA-directed 5′-3′ RNA polymerase activity”, with various categories linked to “binding” evidencing significant homopeptide depletions. Also, in general homopeptides are substantially enriched in the parts of protein domains that are near/in IDRs. The implications of these findings are discussed.

Comparative proteomics uncovers low asparagine insertion inPlasmodiumtRip-KO proteins

“…However, a non-specific Northern Blot probe hybridizing both endogenous parasite tRNAs and imported host tRNAs showed that, despite their excessive use in protein translation, P. falciparum tRNA Asn does not accumulate more than other tRNAs in the blood stages of the parasite (21). This observation is in line with our hypothesis that insertions, and especially asparagine-rich insertions, could regulate ribosome translation rates and influence protein co-translational folding (22,23). Here, we propose that the import of host tRNA Asn enables the decoding of such asparagine-rich sequences.…”