Abstract
Ricin belongs to the group of ribosome-inactivating proteins (RIPs), i.e., toxins that have evolved to provide particular species with an advantage over other competitors in nature. Ricin possesses RNA N-glycosidase activity enabling the toxin to eliminate a single adenine base from the sarcin-ricin RNA loop (SRL), which is a highly conserved structure present on the large ribosomal subunit in all species from the three domains of life. The SRL belongs to the GTPase associated center (GAC), i.e., a ribosomal element involved in conferring unidirectional trajectory for the translational apparatus at the expense of GTP hydrolysis by translational GTPases (trGTPases). The SRL represents a critical element in the GAC, being the main triggering factor of GTP hydrolysis by trGTPases. Enzymatic removal of a single adenine base at the tip of SRL by ricin blocks GTP hydrolysis and, at the same time, impedes functioning of the translational machinery. Here, we discuss the consequences of SRL depurination by ricin for ribosomal performance, with emphasis on the mechanistic model overview of the SRL modus operandi.
Highlights
Toxic proteins are naturally present in a wide variety of species [1]
The many translation process to proceed efficiently and to comply with the metabolic needs of the cell requires protein factors, which sequentially guide the ribosome through the protein synthesis requires many protein factors, which sequentially guide the ribosome through the protein synthesis cycle
The sarcin–ricin loop (SRL) has been found as a primary target for ricin and other ribosome-inactivating proteins (RIPs), and the specificity of the interaction with eukaryotic ribosomal proteins plays a critical role in ricin catalytic activity towards SRL
Summary
Toxic proteins are naturally present in a wide variety of species [1]. It is thought that they have evolved to play a specific role in defense against animals, pathogens, and various insects, giving advantage in a particular niche [2,3]. The mechanism of toxicity of plant toxins is of great interest because they are present in human foods [4,5] and used in ethnomedicine [6] and cosmetics [7] They have attracted attention in broad biotechnological applications [8,9]. Regardless of the docking element, the eukaryotic ribosomal proteins are considered as guide molecules for RIPs, directing and activating the toxin toward its catalytic target - the SRL. We are presenting the current understanding of the structure and function of SRL during the translational cycle, with particular focus on the molecular consequences of ricin-dependent adenine base removal on ribosome performance
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