Crystal structure of the EndoG/EndoGI complex: mechanism of EndoG inhibition.
EndoG is a ubiquitous nuclease that is translocated into the nucleus during apoptosis to participate in DNA degradation. The enzyme cleaves double- and single-stranded DNA and RNA. Related nucleases are found in eukaryotes and prokaryotes, which have evolved sophisticated mechanisms for genome protection against self-antagonizing nuclease activity. Common mechanisms of inhibition are secretion, sequestration into a separate cellular compartment or by binding to protein inhibitors. Although EndoG is silenced by compartmentalization into the mitochondrial intermembrane space, a nucleus-localized protein inhibitor protects cellular polynucleotides from degradation by stray EndoG under non-apoptotic conditions in Drosophila. Here, we report the first three-dimensional structure of EndoG in complex with its inhibitor EndoGI. Although the mechanism of inhibition is reminiscent of bacterial protein inhibitors, EndoGI has evolved independently from a generic protein-protein interaction module. EndoGI is a two-domain protein that binds the active sites of two monomers of EndoG, with EndoG being sandwiched between EndoGI. Since the amino acid sequences of eukaryotic EndoG homologues are highly conserved, this model is valid for eukaryotic dimeric EndoG in general. The structure indicates that the two active sites of EndoG occupy the most remote spatial position possible at the molecular surface and a concerted substrate processing is unlikely.
Department of Biomolecular Mechanisms, Max Planck Institute for Medical Research, Jahnstrasse 29, 69120 Heidelberg, Germany.
Bernhard
B
Loll
Maike
M
Gebhardt
Elmar
E
Wahle
Anton
A
Meinhart
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D020134:Catalytic Domain; D017124:Conserved Sequence; D003461:Crystallography; D019281:Dimerization; D029721:Drosophila Proteins / Q000737:chemistry*; D004331:Drosophila melanogaster / Q000201:enzymology*; D004706:Endodeoxyribonucleases / Q000737:chemistry*; D004791:Enzyme Inhibitors / Q000737:chemistry*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009841:Oligonucleotides / Q000737:chemistry
D029721:Drosophila Proteins; D004791:Enzyme Inhibitors; D009841:Oligonucleotides; D004706:Endodeoxyribonucleases; C052391:endonuclease G