Structural mechanism for inactivation and activation of CAD/DFF40 in the apoptotic pathway.
CAD/DFF40 is responsible for the degradation of chromosomal DNA into nucleosomal fragments and subsequent chromatin condensation during apoptosis. It exists as an inactive complex with its inhibitor ICAD/DFF45 in proliferating cells but becomes activated upon cleavage of ICAD/DFF45 into three domains by caspases in dying cells. The molecular mechanism underlying the control and activation of CAD/DFF40 was unknown. Here, the crystal structure of activated CAD/DFF40 reveals that it is a pair of molecular scissors with a deep active-site crevice that appears ideal for distinguishing internucleosomal DNA from nucleosomal DNA. Ensuing studies show that ICAD/DFF45 sequesters the nonfunctional CAD/DFF40 monomer and is also able to disassemble the functional CAD/DFF40 dimer. This capacity requires the involvement of the middle domain of ICAD/DFF45, which by itself cannot remain bound to CAD/DFF40 due to low binding affinity for the enzyme. Thus, the consequence of the caspase-cleavage of ICAD/DFF45 is a self-assembly of CAD/DFF40 into the active dimer.
Woo
Eui-Jeon
EJ
Division of Molecular and Life Sciences, Department of Life Sciences and Center for Biomolecular Recognition, Pohang University of Science and Technology, Pohang, Kyungbuk 790-784, South Korea.
Kim
Yeon-Gil
YG
Kim
Min-Sung
MS
Han
Won-Deok
WD
Shin
Sejeong
S
Robinson
Howard
H
Park
Sam-Yong
SY
Oh
Byung-Ha
BH
D000595:Amino Acid Sequence / Q000502:physiology; D017209:Apoptosis / Q000502:physiology*; D051017:Apoptosis Regulatory Proteins; D001665:Binding Sites / Q000502:physiology; D020169:Caspases / Q000378:metabolism; D020134:Catalytic Domain / Q000502:physiology; D004247:DNA / Q000235:genetics / Q000378:metabolism*; D053938:DNA Fragmentation / Q000235:genetics / Q000502:physiology*; D003851:Deoxyribonucleases / Q000737:chemistry* / Q000378:metabolism*; D019281:Dimerization; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009707:Nucleosomes / Q000378:metabolism; D011485:Protein Binding / Q000502:physiology; D020836:Protein Structure, Quaternary / Q000502:physiology; D011506:Proteins / Q000378:metabolism; D015032:Zinc / Q000378:metabolism
D051017:Apoptosis Regulatory Proteins; D009707:Nucleosomes; D011506:Proteins; C109664:caspase-activated DNase inhibitor; D004247:DNA; D003851:Deoxyribonucleases; C109663:caspase-activated deoxyribonuclease; D020169:Caspases; D015032:Zinc