BtubA-BtubB Heterodimer Is an Essential Intermediate in Protofilament Assembly
Figure 5
Between-dimer mutants disassemble wild type polymers by sequestering subunits into inactive heterodimers.
The equilibrium on the left shows wild type BtubA/B protofilaments exchanging with dimers. These dimers are also exchanging with a small pool of monomers, not shown. The bracket on the right shows what happens when the reaction is flooded with between-dimer BtubB subunits. These are capable of forming dimers, and because they are in excess of the monomer/dimer pool they will replace the wild type BtubB. This sequesters most of the wild type BtubA into inactive dimers. This depletion of wild type dimers to below the critical concentration results in depolymerization.