1. Evidence for the importance of electrostatics in the function of two distinct families of ribosome inactivating toxins.
- Author
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Korennykh AV, Correll CC, and Piccirilli JA
- Subjects
- Endoribonucleases physiology, Fungal Proteins physiology, N-Glycosyl Hydrolases classification, Plant Proteins classification, Protein Synthesis Inhibitors pharmacology, Ribosome Inactivating Proteins, Type 1, Ribosomes chemistry, Ricin classification, Ricin pharmacology, Saporins, Static Electricity, Sulfuric Acid Esters classification, Sulfuric Acid Esters pharmacology, Surface Properties, Triterpenes classification, Triterpenes pharmacology, Endoribonucleases chemistry, Fungal Proteins chemistry, Multigene Family physiology, N-Glycosyl Hydrolases chemistry, N-Glycosyl Hydrolases physiology, Plant Proteins chemistry, Plant Proteins physiology, Protein Synthesis Inhibitors chemistry, Ribosomes metabolism, Ricin chemistry, Sulfuric Acid Esters chemistry, Triterpenes chemistry
- Abstract
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.
- Published
- 2007
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