The association of a La module with the PABP-interacting motif PAM2 is a recurrent evolutionary process that led to the neofunctionalization of La-related proteins

La-related proteins (LARPs) are largely uncharacterized factors, well conserved throughout evolution. Recent reports on the function of human LARP4 and LARP6 suggest that these proteins fulfill key functions in mRNA metabolism and/or translation. We report here a detailed evolutionary history of the LARP4 and 6 families in eukaryotes. Genes coding for LARP4 and 6 were duplicated in the common ancestor of the vertebrate lineage, but one LARP6 gene was subsequently lost in the common ancestor of the eutherian lineage. The LARP6 gene was also independently duplicated several times in the vascular plant lineage. We observed that vertebrate LARP4 and plant LARP6 duplication events were correlated with the acquisition of a PABP-interacting motif 2 (PAM2) and with a significant reorganization of their RNA-binding modules. Using isothermal titration calorimetry (ITC) and immunoprecipitation methods, we show that the two plant PAM2-containing LARP6s (LARP6b and c) can, indeed, interact with the major plant poly(A)-binding protein (PAB2), while the third plant LARP6 (LARP6a) is unable to do so. We also analyzed the RNA-binding properties and the subcellular localizations of the two types of plant LARP6 proteins and found that they display nonredundant characteristics. As a whole, our results support a model in which the acquisition by LARP4 and LARP6 of a PAM2 allowed their targeting to mRNA 3' UTRs and led to their neofunctionalization.

Identification and functional characterization of a poly(A)-binding protein from Leishmania infantum (LiPABP)

Gene expression regulation in Leishmania has been related to post-transcriptional events involving mainly sequences present in the 5' and 3' untranslated regions. PABPs are high-affinity poly(A)-binding proteins that are implicated in the regulation of translation initiation, RNA stability and other important biological processes. We describe a PABP from Leishmania infantum (LiPABP) that shows a very high homology with PABPs from other eukaryotic organisms, including mammals and other parasites. LiPABP conserves the main domains present in other PABPs, maintains poly(A)-binding properties and is phosphorylated by p38 mitogen-activated protein kinase. Using the sera from dogs infected with L. infantum, we demonstrate that LiPABP is expressed in L. infantum promastigotes.