Crystal structure of RNase A tandem enzymes and their interaction with the cytosolic ribonuclease inhibitor.

Ulrich Arnold, Franziska Leich, Piotr Neumann, Hauke Lilie, Renate Ulbrich-Hofmann

Department of Biochemistry and Biotechnology, Martin-Luther University Halle-Wittenberg, Halle, Germany. ulrich.arnold@biochemtech.uni-halle.de

The FEBS journal 2011 Jan

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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. © 2010 The Authors Journal compilation © 2010 FEBS.

Citation

Ulrich Arnold, Franziska Leich, Piotr Neumann, Hauke Lilie, Renate Ulbrich-Hofmann. Crystal structure of RNase A tandem enzymes and their interaction with the cytosolic ribonuclease inhibitor. The FEBS journal. 2011 Jan;278(2):331-40