However, chemical modification analysis could not distinguish between the roles of these residues in substrate binding catalytic activity and did not provide direct evidence for his or her involvement in substrate binding. although the activity against rat rRNA is about 5 orders 5-Methylcytidine of magnitude lower than against intact rat ribosomes (6). In contrast to ricin, additional RIPs, such as Stx and pokeweed antiviral protein, are 5-Methylcytidine equally active on eukaryotic and prokaryotic ribosomes (16). These studies suggested that ricin and related RIPs may require docking to ribosomal proteins to keep up an ideal depurination rate (17). We showed that RTA binds to a component of the large ribosomal subunit known as the ribosomal P-protein stalk to depurinate the SRL in candida (18, 19) and in human being cells (20). RTA interacts directly with isolated put together P-protein stalk complexes from candida (21). The ribosomal stalk is definitely a 5-Methylcytidine lateral protuberance of the large ribosome subunit, which recruits elongation element 2 and additional GTPase factors to the ribosome and stimulates factor-dependent GTP hydrolysis during translation (22, 23). In eukaryotes, it forms a pentameric structure, consisting of a P0 protein, which anchors two P1-P2 heterodimers (24, 25). Rabbit Polyclonal to SFXN4 The unique feature of all P-proteins is the C-terminal 11 amino acids, which are identical in all eukaryotes and are probably involved in direct connection with the translation factors (26C28). The mechanism of their connection with the translation factors is not well understood. Earlier studies showed that trichosanthin (TCS), a single chain RIP (29), and the A1 chain of Shiga toxin 1 (Stx1) (30, 31) interact with the conserved CTD fragment of P0, P1, and P2. A recent solution structure of the full-length P1/P2 heterodimer showed a helical N-terminal website and an unstructured C-terminal tail, which is required for the depurination activity of TCS (32). The structure of a peptide corresponding to the last 11 amino acids of the stalk proteins inside a complex with TCS has been determined (33). Relating to this structure, the acidic amino acids in the amino end of the peptide interact with the positively charged Lys173, Arg174, and Lys177 of TCS, whereas the hydrophobic part of the carboxyl end of the peptide is definitely inserted into a hydrophobic pocket of TCS (33). The amino acids that interact with P2 protein are located inside a different region of the maize RIP than in TCS and differ in main sequence and electrostatic distribution (34). It has been suggested that the ability to interact with the stalk arose individually by convergent development (35). Kinetic analysis of binding showed that five identical C termini of the stalk proteins increase the association rate of the connection between RTA and the stalk (21). Moreover, RTA may undergo a conformational switch upon depurination (36). These results suggest that the connection of RTA with the stalk is definitely a dynamic process, which cannot be fully explained by x-ray structure analysis. Residues involved in ribosome binding of RTA have not been identified. Chemical modification analysis showed that RTA lost its activity in cell-free protein synthesis when only a few arginines were altered by phenylglyoxal and that this inactivation was reversible (37). Changes of arginines at positions 193, 196, 213, and 234/235, which are primarily located on the reverse part of the active site cleft, decreased the pace of depurination and the affinity for the ribosome without causing a detectable switch in the conformation of the catalytic site (38). Deletion analysis showed that Arg193, Arg196, and Arg197 were important for the activity of RTA (39). However, chemical modification analysis could not distinguish between the roles of these residues in substrate binding catalytic activity and did not provide direct evidence for their involvement in substrate binding. Most 5-Methylcytidine of the surface residues of RTA were thought to be directly or indirectly involved in the connection of RTA with ribosomes, and substitution of only a few residues was thought not to possess a sufficient effect on the connection (39). In the present study, we made point mutations at arginines at or near the interface of RTA and RTB and identified the effect of these mutations on ribosome binding and catalytic activity of RTA. Our findings identify for the first time RTA residues critical for binding to the P-protein stalk but not for catalytic activity and display the ribosome binding surface of RTA is definitely on the opposite side of the active site cleft. These results provide novel information about the molecular action of RTA and may become.
