Mechanistic insights into CED-4-mediated activation of CED-3.
Programmed cell death in Caenorhabditis elegans requires activation of the caspase CED-3, which strictly depends on CED-4. CED-4 forms an octameric apoptosome, which binds the CED-3 zymogen and facilitates its autocatalytic maturation. Despite recent advances, major questions remain unanswered. Importantly, how CED-4 recognizes CED-3 and how such binding facilitates CED-3 activation remain completely unknown. Here we demonstrate that the L2' loop of CED-3 directly binds CED-4 and plays a major role in the formation of an active CED-4-CED-3 holoenzyme. The crystal structure of the CED-4 apoptosome bound to the L2' loop fragment of CED-3, determined at 3.2 Å resolution, reveals specific interactions between a stretch of five hydrophobic amino acids from CED-3 and a shallow surface pocket within the hutch of the funnel-shaped CED-4 apoptosome. Structure-guided biochemical analysis confirms the functional importance of the observed CED-4-CED-3 interface. Structural analysis together with published evidence strongly suggest a working model in which two molecules of CED-3 zymogen, through specific recognition, are forced into the hutch of the CED-4 apoptosome, consequently undergoing dimerization and autocatalytic maturation. The mechanism of CED-3 activation represents a major revision of the prevailing model for initiator caspase activation.
Ministry of Education Protein Science Laboratory, Center for Structural Biology, School of Life Sciences.
Weijiao
W
Huang
Tianyu
T
Jiang
Wooyoung
W
Choi
Shiqian
S
Qi
Yuxuan
Y
Pang
Qi
Q
Hu
Yanhui
Y
Xu
Xinqi
X
Gong
Philip D
PD
Jeffrey
Jiawei
J
Wang
Yigong
Y
Shi
D000596:Amino Acids / Q000737:chemistry; D000818:Animals; D017173:Caenorhabditis elegans; D029742:Caenorhabditis elegans Proteins / Q000737:chemistry* / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000737:chemistry* / Q000378:metabolism*; D020169:Caspases / Q000737:chemistry* / Q000378:metabolism*; D003460:Crystallization; D004789:Enzyme Activation; D008958:Models, Molecular; D011485:Protein Binding; D055550:Protein Stability; D020836:Protein Structure, Quaternary
D000596:Amino Acids; D029742:Caenorhabditis elegans Proteins; D002135:Calcium-Binding Proteins; C089224:Ced-4 protein, C elegans; D020169:Caspases; C089223:ced-3 protein, C elegans
CED-3; CED-4; apoptosis; caspase activation; programmed cell death (PCD)