3MWQ: Crystal Structure Of Ribonuclease 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.
PDB ID: 3MWQDownload
MMDB ID: 88497
PDB Deposition Date: 2010/5/6
Updated in MMDB: 2017/06
Experimental Method:
x-ray diffraction
Resolution: 1.68  Å
Source Organism:
Similar Structures:
Biological Unit for 3MWQ: monomeric; determined by author and by software (PISA)
Molecular Components in 3MWQ
Label Count Molecule
Protein (1 molecule)
Ribonuclease Pancreatic, Linker, Ribonuclease Pancreatic(Gene symbol: RNASE1)
Molecule annotation
Chemicals (7 molecules)
* Click molecule labels to explore molecular sequence information.

Citing MMDB