Adaptive and Conservative Protein Assets In Plasmodia. Two Different Scenarios of the Biology of Malaria Parasites

The evolutionary origin of Low Complexity Sequences (LCSs) inside the proteome of P. falciparum, the agent of the most virulent form of human malaria, is still an argument of debate. It is poorly understood whether they come from selective pressure or from mutational bias. Taking as reference several other plasmodium species and dividing each proteome in two subclasses, i.e. the Low Complexity Containing Proteins (LCPs) namely those proteins that contain at least one LCR inside their chain, and not Low Complexity Containing Proteins (nLCPs) that contain none, we find several evidences that address the LCPs as recently evolutionary emerged proteins and nLCPs as the more conserved proteins in plasmodia. The former category result to be composed by significantly longer proteins with respect to the latter. Together with the implementation of another well known bioinformatic tool The Effective Number of Codons (ENCs) and a new index that here we call the SPI (Selective Pressure Index) we find a major meddling of mutational bias on LCPs. On the other hand, the purifying pressure appears to restrain codon usage patterns in nLCPs. Our data in line with other results found in literature shows how LCPs represent an evolutionary nuance and a signal of adaptation and evolutionary path. Symmetrically, nLCPs could represent a core asset for the maintenance of parasite fitness.