Association of RACK1 protein with ribosomes in Plasmodium falciparum

The receptor for activated C-kinase 1 (RACK1), a highly conserved eukaryotic protein, is known to have many, varying biological roles and functions. Previous work has established RACK1 as a ribosomal protein, with defined regions important for binding ribosomes in both human and yeast cells. In Plasmodium falciparum, RACK1 has been shown to be required for parasite growth, however conflicting evidence has been presented about the RACK1 ribosome binding and its role in mRNA translation. Given the importance of RACK1 as a regulatory component of mRNA translation and ribosome quality control, the case could be made in parasites for either of the binary options: bound or unbound to the ribosome. Here we used bioinformatics and transcription analyses to describe P. falciparum RACK1 protein. Based on homology modeling and structural analyses, we generated a model of P. falciparum RACK1 protein. We created and explored mutant and chimeric human and P. falciparum RACK1 proteins binding properties to the human and P. falciparum ribosome. Wild type, chimeric and mutant RACK1 proteins suggest different binding characteristics for P. falciparum and human RACK1 proteins and different regions being involved in their ribosome association. The ribosomal binding of RACK1 variants in human and parasite cells shown here demonstrates that although RACK1 proteins have highly conserved sequences and structures across species, ribosomal binding is affected by species specific alterations to the protein. In conclusion, we show that in the case of P. falciparum, contrary to the structural data, RACK1 is found to be bound to ribosomes and in actively translating polysomes of P. falciparum cells.