期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2014
卷号：111
期号：46
页码：16254-16261
DOI：10.1073/pnas.1418000111
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceUpstream cell death stimuli culminate in the activation of an initiator caspase, marking the onset of apoptosis. Activation of the initiator caspase, caspase-9, is mediated by the heptameric Apaf-1 apoptosome. How Apaf-1 apoptosome facilitates the autocatalytic activation of caspase-9 has remained controversial and largely enigmatic. Two contrasting but not mutually exclusive hypotheses, proximity-induced dimerization vs. induced conformation, emphasize different aspects of initiator caspase activation. This study provides compelling evidence to support the induced conformation model for caspase-9 activation. A previously unknown interface between Apaf-1 and caspase-9 was identified to play an essential role in caspase-9 activation, and formation of a multimeric complex between Apaf-1 caspase recruitment domain (CARD) and caspase-9 was shown to be indispensable for caspase-9 activation. Autocatalytic activation of an initiator caspase triggers the onset of apoptosis. In dying cells, caspase-9 activation is mediated by a multimeric adaptor complex known as the Apaf-1 apoptosome. The molecular mechanism by which caspase-9 is activated by the Apaf-1 apoptosome remains largely unknown. Here we demonstrate that the previously reported 1:1 interaction between Apaf-1 caspase recruitment domain (CARD) and caspase-9 CARD is insufficient for the activation of caspase-9. Rather, formation of a multimeric CARD:CARD assembly between Apaf-1 and caspase-9, which requires three types of distinct interfaces, underlies caspase-9 activation. Importantly, an additional surface area on the multimeric CARD assembly is essential for caspase-9 activation. Together, these findings reveal mechanistic insights into the activation of caspase-9 by the Apaf-1 apoptosome and support the induced conformation model for initiator caspase activation by adaptor complexes.
