2VFX

Insights Into MAD2 Regulation in the Spindle Checkpoint Revealed by the Crystal Structure of the Symmetric MAD2 Dimer.

(2008) PLoS Biol 6: E50

• PubMed: 18318601 Search on PubMedSearch on PubMed Central
• DOI: https://doi.org/10.1371/journal.pbio.0060050
• Primary Citation of Related Structures:  
  2VFX


• PubMed 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.

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Organizational Affiliation: 

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