title: Evidence for the importance of electrostatics in the function of two distinct families of ribosome inactivating toxins.
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.
authors.forename: Alexei V
authors.initials: AV
authors.lastname: Korennykh
authors.forename: Carl C
authors.initials: CC
authors.lastname: Correll
authors.forename: Joseph A
authors.initials: JA
authors.lastname: Piccirilli
mesh_terms: D004722:Endoribonucleases / Q000737:chemistry* / Q000502:physiology; D005656:Fungal Proteins / Q000737:chemistry* / Q000502:physiology; D005810:Multigene Family / Q000502:physiology*; D009699:N-Glycosyl Hydrolases / Q000737:chemistry* / Q000145:classification / Q000502:physiology*; D010940:Plant Proteins / Q000737:chemistry* / Q000145:classification / Q000502:physiology*; D011500:Protein Synthesis Inhibitors / Q000737:chemistry* / Q000494:pharmacology; D054789:Ribosome Inactivating Proteins, Type 1; D012270:Ribosomes / Q000737:chemistry / Q000378:metabolism*; D012276:Ricin / Q000737:chemistry* / Q000145:classification / Q000494:pharmacology; D000076985:Saporins; D055672:Static Electricity; D013463:Sulfuric Acid Esters / Q000737:chemistry* / Q000145:classification / Q000494:pharmacology; D013499:Surface Properties; D014315:Triterpenes / Q000737:chemistry* / Q000145:classification / Q000494:pharmacology
chemical_list: C520867:3-O-(sulfo)lup-20(29)-en-23,28-dioic acid; D005656:Fungal Proteins; D010940:Plant Proteins; D011500:Protein Synthesis Inhibitors; D054789:Ribosome Inactivating Proteins, Type 1; D013463:Sulfuric Acid Esters; D014315:Triterpenes; C014801:alpha-sarcin; D012276:Ricin; D004722:Endoribonucleases; D009699:N-Glycosyl Hydrolases; D000076985:Saporins