The spindle checkpoint delays chromosome segregation in response to misaligned sister chromatids during mitosis, thus ensuring the fidelity of chromosome inheritance. Through binding to Cdc20, the Mad2 spindle checkpoint protein inhibits the target of this checkpoint, the ubiquitin protein ligase APC/C(Cdc20) ...
The spindle checkpoint delays chromosome segregation in response to misaligned sister chromatids during mitosis, thus ensuring the fidelity of chromosome inheritance. Through binding to Cdc20, the Mad2 spindle checkpoint protein inhibits the target of this checkpoint, the ubiquitin protein ligase APC/C(Cdc20). We now show that without cofactor binding or covalent modification Mad2 adopts two distinct folded conformations at equilibrium (termed N1-Mad2 and N2-Mad2). The structure of N2-Mad2 has been determined by NMR spectroscopy. N2-Mad2 is much more potent in APC/C inhibition. Overexpression of a Mad2 mutant that specifically sequesters N2-Mad2 partially blocks checkpoint signaling in living cells. The two Mad2 conformers interconvert slowly in vitro, but interconversion is accelerated by a fragment of Mad1, an upstream regulator of Mad2. Our results suggest that the unusual two-state behavior of Mad2 is critical for spindle checkpoint signaling.
Related Citations:
Structure of the Mad2 spindle assembly checkpoint protein and its interaction with Cdc20 Luo, X., Fang, G., Coldiron, M., Lin, Y., Yu, H., Kirschner, M.W., Wagner, G. (2000) Nat Struct Biol 7: 224
The Mad2 Spindle Checkpoint Protein Undergoes Similar Major Conformational Changes upon Binding to Either Mad1 or Cdc20 Luo, X., Tang, Z., Rizo, J., Yu, H. (2002) Mol Cell 9: 59
Organizational Affiliation:
Department of Pharmacology, The University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, Texas 75390, USA.
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