Format

Send to

Choose Destination
See comment in PubMed Commons below
PLoS Biol. 2008 Mar 4;6(3):e50. doi: 10.1371/journal.pbio.0060050.

Insights into mad2 regulation in the spindle checkpoint revealed by the crystal structure of the symmetric mad2 dimer.

Author information

1
Department of Pharmacology, The University of Texas Southwestern Medical Center, Dallas, Texas, United States of America.

Abstract

In response to misaligned sister chromatids during mitosis, the spindle checkpoint protein Mad2 inhibits the anaphase-promoting complex or cyclosome (APC/C) through binding to its mitotic activator Cdc20, thus delaying anaphase onset. Mad1, an upstream regulator of Mad2, forms a tight core complex with Mad2 and facilitates Mad2 binding to Cdc20. In the absence of its binding proteins, free Mad2 has two natively folded conformers, termed N1-Mad2/open-Mad2 (O-Mad2) and N2-Mad2/closed Mad2 (C-Mad2), with C-Mad2 being more active in APC/C(Cdc20) inhibition. Here, we show that whereas O-Mad2 is monomeric, C-Mad2 forms either symmetric C-Mad2-C-Mad2 (C-C) or asymmetric O-Mad2-C-Mad2 (O-C) dimers. We also report the crystal structure of the symmetric C-C Mad2 dimer, revealing the basis for the ability of unliganded C-Mad2, but not O-Mad2 or liganded C-Mad2, to form symmetric dimers. A Mad2 mutant that predominantly forms the C-C dimer is functional in vitro and in living cells. Finally, the Mad1-Mad2 core complex facilitates the conversion of O-Mad2 to C-Mad2 in vitro. Collectively, our results establish the existence of a symmetric Mad2 dimer and provide insights into Mad1-assisted conformational activation of Mad2 in the spindle checkpoint.

PMID:
18318601
PMCID:
PMC2270309
DOI:
10.1371/journal.pbio.0060050
[Indexed for MEDLINE]
Free PMC Article
PubMed Commons home

PubMed Commons

0 comments
How to join PubMed Commons

    Supplemental Content

    Full text links

    Icon for Public Library of Science Icon for PubMed Central
    Loading ...
    Support Center