Evidence for the importance of electrostatics in the function of two distinct families of ribosome inactivating toxins.

Alexei V Korennykh, Carl C Correll, Joseph A Piccirilli

RNA (New York, N.Y.) 2007 Sep

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Alpha-sarcin and ricin represent two structurally and mechanistically distinct families of site-specific enzymes that block translation by irreversibly modifying the sarcin/ricin loop (SRL) of 23S-28S rRNA. alpha-Sarcin family enzymes are designated as ribotoxins and act as endonucleases. Ricin family enzymes are designated as ribosome inactivating proteins (RIP) and act as N-glycosidases. Recently, we demonstrated that basic surface residues of the ribotoxin restrictocin promote rapid and specific ribosome targeting by this endonuclease. Here, we report that three RIP: ricin A, saporin, and gypsophilin depurinate the ribosome with strong salt sensitivity and achieve unusually fast kcat/Km approximately 10(9)-10(10) M(-1) s(-1), implying that RIP share with ribotoxins a common mechanism of electrostatically facilitated ribosome targeting. Bioinformatics analysis of RIP revealed that surface charge properties correlate with the presence of the transport chain in the RIP molecule, suggesting a second role for the surface charge in RIP transport. These findings put forward surface electrostatics as an important determinant of RIP activity.

Citation

Alexei V Korennykh, Carl C Correll, Joseph A Piccirilli. Evidence for the importance of electrostatics in the function of two distinct families of ribosome inactivating toxins. RNA (New York, N.Y.). 2007 Sep;13(9):1391-6