Molecular determinants of caspase-9 activation by the Apaf-1 apoptosome

Area of Science:

• Cellular biology
• Molecular mechanisms of apoptosis

Background:

• Apoptosis, or programmed cell death, is initiated by autocatalytic caspase activation.
• Caspase-9 activation in dying cells is mediated by the Apaf-1 apoptosome adaptor complex.
• The precise mechanism of caspase-9 activation by the Apaf-1 apoptosome is not fully understood.

Purpose of the Study:

• To elucidate the molecular mechanism of caspase-9 activation by the Apaf-1 apoptosome.
• To investigate the role of the interaction between Apaf-1 and caspase-9.
• To determine the structural requirements for caspase-9 activation.

Main Methods:

• Investigated the interaction between Apaf-1 and caspase-9.
• Analyzed the formation of caspase recruitment domain (CARD):CARD assemblies.
• Characterized the interfaces and surface areas involved in multimeric complex formation.

Main Results:

• A 1:1 interaction between Apaf-1 CARD and caspase-9 CARD is insufficient for caspase-9 activation.
• Caspase-9 activation requires the formation of a multimeric CARD:CARD assembly between Apaf-1 and caspase-9.
• This multimeric assembly necessitates three distinct interfaces and an additional surface area for effective caspase-9 activation.

Conclusions:

• The activation of caspase-9 by the Apaf-1 apoptosome is mediated by a multimeric CARD:CARD assembly.
• Specific interfaces and surface areas within this assembly are critical for inducing caspase-9 activation.
• Findings support the induced conformation model for initiator caspase activation by adaptor complexes, providing mechanistic insights into apoptosis regulation.