Alternative models about the origin of Ribosome Inactivating Protein genes

LAPADULA, W; SÁNCHEZ PUERTA, M. V.; JURI AYUB, M

Oro Verde, Entre Rios

Congreso; 3er Congreso Argentino de Bioinformática y Biología Computacional.; 2012

Asociacion Argentina de Bioinformatica y Biologia Computacional

Ribosome inactivating proteins (RIPs) are N-glycosidases that depurinate a specific adenine residue in the conserved sarcin/ricin loop of 28S rRNA. The most widely studied examples of RIPs are ricin, a potent toxin of Ricinus communis, and Shiga toxins from enteric bacteria causing hemolytic uremic syndrome. RIPs genes have been reported to be present in many plants and a few bacteria. In addition, there are biochemical evidences of RIP activity in a few fungi species. The analysis of RIPs phylogeny is problematic because the sequences are highly divergent, and their distribution across species is patchily distributed. It is currently assumed that RIPs genes were originated in plants and prokaryotic RIPs have been acquired by a single Horizontal Gene Transfer (HGT) event from plant to bacteria [1]. We have recently reported a phylogenetic analysis of RIP sequences [2]. In the present work, we performed exhaustive searches for novel RIP genes in genomic and EST databases. We found novel RIP encoding sequences from bacteria, and more interestingly, eleven RIP genes in fungal WGS. These results suggest that the current view of RIPs phylogeny should be revisited. Therefore, we performed sequence alignments using different algorithms (CLUSTALW, T-COFEE, MAFFT), and new phylogeny inferences including the novel sequences. The resulting data were analyzed in the context of phylogenetic relationships among species, in order to propose the most plausible hypothesis. Altogether, the data can be explained by at least two alternative models (see Figure 1): I. RIPs genes originated in plants and were acquired via HGT by fungi and bacteria. This model implies at least three independent HGT events. II. RIPs genes were present in the common ancestor of eukaryotes and bacteria, and were lost in several lineages through evolution. This model implies several loss events in different lineages; archaea, metazoan, many bacteria, etc. The pros and cons of these models are discussed in this work.