Escape from the checkpoint: Nek2A binds a unique conformation of the APC/C-MCC complex

Area of Science:

• Cellular biology
• Molecular mechanisms of cell division
• Protein degradation pathways

Background:

• Cell division relies on precise protein degradation orchestrated by the anaphase-promoting complex/cyclosome (APC/C).
• The APC/C, an E3 ubiquitin ligase, targets substrates via degrons when complexed with Cdc20.
• The mitotic checkpoint complex (MCC) inhibits APC/C-Cdc20, enforcing a 'wait anaphase' signal.

Discussion:

• The mitotic kinase Nek2A bypasses MCC inhibition, a previously unexplained phenomenon.
• Alfieri and colleagues reveal Nek2A binds a specific open conformation of the APC/C-MCC complex.
• This interaction allows Nek2A ubiquitination independently of canonical degrons.

Key Insights:

• Nek2A, as a dimer, utilizes C-terminal MR motifs to bind two distinct pockets on the APC/C.
• One binding pocket is accessible only in the open APC/C-MCC conformation, conferring Nek2A's selectivity.
• This mechanism explains how Nek2A avoids MCC-mediated inhibition during cell division.

Outlook:

• Investigating whether other APC/C substrates also bind directly, bypassing canonical degrons.
• Understanding the structural basis of Nek2A's interaction with the open APC/C-MCC conformation.
• Exploring the broader implications for cell cycle regulation and protein degradation control.