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Timing of APC/C substrate degradation is determined by fzy/fzr specificity of destruction boxes

Amit Zur1, Michael Brandeis

  • 1Department of Genetics, Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, Jerusalem 91904, Israel.

The EMBO Journal
|August 29, 2002
PubMed

Insights

The anaphase-promoting complex/cyclosome (APC/C) controls cell cycle timing by degrading proteins. This study reveals how destruction boxes (d-boxes) dictate APC/C specificity and degradation order, ensuring proper cell division.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Biochemistry

Background:

  • The anaphase-promoting complex/cyclosome (APC/C) is a crucial ubiquitin ligase complex regulating cell cycle progression.
  • APC/C activity is tightly controlled by its co-activators, Cdc20 (encoded by fzy) and Cdh1 (encoded by fzr).
  • APC/C substrates contain specific destruction motifs, RXXL or KEN boxes (d-boxes), which are recognized by the APC/C-coactivator complex.

Purpose of the Study:

  • To investigate how different destruction boxes (d-boxes) confer substrate specificity to APC/C-fzy and APC/C-fzr complexes.
  • To determine how d-box sequences and APC/C co-activator specificity influence the timing of substrate degradation during mitosis and G1.
  • To elucidate the mechanisms underlying the ordered degradation of APC/C substrates.

Main Methods:

  • Utilized in vivo degradation assays with real-time monitoring of tagged substrates.
  • Employed site-directed mutagenesis to swap destruction box motifs (RXXL and KEN) in known APC/C substrates like Cyclin B1 and fzy.
  • Analyzed the degradation kinetics of wild-type and mutant substrates by APC/C-fzy and APC/C-fzr complexes.

Main Results:

  • Substrate degradation by APC/C-fzy and APC/C-fzr is d-box dependent, with RXXL and KEN boxes conferring distinct specificities.
  • Cyclin B1 (RXXL) is degraded by both APC/C-fzy and APC/C-fzr, while fzy (KEN box) is degraded only by APC/C-fzr.
  • Degradation mediated by APC/C-fzy is highly sensitive to the RXXL motif's position, whereas APC/C-fzr exhibits broader substrate acceptance.
  • APC/C-fzr activation occurs in early G1, contributing to the temporal separation of degradation events.

Conclusions:

  • The specificity of d-boxes for APC/C-fzy and APC/C-fzr, coupled with the sequential activation of APC/C by fzy and fzr, establishes the precise temporal degradation pattern of cell cycle proteins.
  • These findings explain why certain endogenous RXXL substrates are exclusively degraded by APC/C-fzy, while others are targeted by APC/C-fzr.
  • Understanding d-box specificity is critical for comprehending cell cycle control and ensuring accurate chromosome segregation and cell division.

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