Crystal structure of RNase A tandem enzymes and their interaction with the cytosolic ribonuclease inhibitor.
Because of their ability to degrade RNA, RNases are potent cytotoxins. The cytotoxic activity of most members of the RNase A superfamily, however, is abolished by the cytosolic ribonuclease inhibitor (RI). RNase A tandem enzymes, in which two RNase A molecules are artificially connected by a peptide linker, and thus have a pseudodimeric structure, exhibit remarkable cytotoxic activity. In vitro, however, these enzymes are still inhibited by RI. Here, we present the crystal structures of three tandem enzymes with the linker sequences GPPG, SGSGSG, and SGRSGRSG, which allowed us to analyze the mode of binding of RI to the RNase A tandem enzymes. Modeling studies with the crystal structures of the RI-RNase A complex and the SGRSGRSG-RNase A tandem enzyme as templates suggested a 1 : 1 binding stoichiometry for the RI-RNase A tandem enzyme complex, with binding of the RI molecule to the N-terminal RNase A entity. These results were experimentally verified by analytical ultracentrifugation, quantitative electrophoresis, and proteolysis studies with trypsin. As other dimeric RNases, which are comparably cytotoxic, either evade RI binding or potentially even bind two RI molecules, inactivation by RI cannot be the crucial limitation to the cytotoxicity of dimeric RNases.
Department of Biochemistry and Biotechnology, Martin-Luther University Halle-Wittenberg, Halle, Germany. ulrich.arnold@biochemtech.uni-halle.de
Ulrich
U
Arnold
Franziska
F
Leich
Piotr
P
Neumann
Hauke
H
Lilie
Renate
R
Ulbrich-Hofmann
D055162:Biocatalysis; D002352:Carrier Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D002852:Chromatography, Ion Exchange; D018360:Crystallography, X-Ray; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D007700:Kinetics; D008958:Models, Molecular; D011485:Protein Binding / Q000502:physiology; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D012313:RNA / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D012259:Ribonuclease, Pancreatic / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D014357:Trypsin / Q000378:metabolism; D014461:Ultracentrifugation
D002352:Carrier Proteins; C501467:RNH1 protein, human; D011993:Recombinant Fusion Proteins; D012313:RNA; D012259:Ribonuclease, Pancreatic; D014357:Trypsin