Phylogenetic and biochemical study of Ribosome Inactivating Proteins

LAPADULA WJ; DUFFY T; REYES LF; SMULSKI CR; GÓMEZ KA; ZÁRATE JM; JURI AYUB M

Mendoza

Congreso; XXVIII Reunión de la sociedad de biología de Cuyo; 2010

Ribosome-inactivating proteins (RIPs) inhibit eukaryotic protein synthesis by depurinating a conserved adenine on the sarcin-ricin loop (SRL). RIPs are classified as type 1 and 2, according to the absence or the presence, respectively, of a lectin chain which mediates toxin cell entry. Despite its well-conserved mechanism of action RIPs have variable activity on non-mammalian ribosomes, which should be related to differential interaction with ribosomal proteins. In this work we perform a phylogenetic analysis of RIP genes and correlate this evolutive information with the biochemical and structural features of RIPs. We show that RIPs inactive against prokaryotic ribosomes are grouped in a separate cluster. This analysis predicted that Mirabilis expansa RIP should be active against E. coli particles (in contrast with previous reports) and therefore experimentally confirmed this prediction. In silico searches led us to identify atypical, catalytically inactive, type 2 RIPs in monocots species distantly related to previously described monocot type 2 RIPs and phylogenetically closer to ricin. The A-chain of one of these RIPs was cloned, expressed in E. coli and characterized. Finally, we correlated the phylogeny of different RIPs with their ability to interact with the ribosomal stalk. In light of these results, we propose that several RIPs during evolution acquired independently the ability to interact with the stalk components, being a case of convergent evolution. Our phylogenetic analysis also allowed us to infer the fusion and deletion events of lectin domain during RIPs evolution.