Dolastatin 10 binds in the "peptide sub-site" of tubulin's vinca domain. Parallelism in Hanes plots indicates that hemiasterlin competitively inhibits dolastatin 10's binding to tubulin; i.e., hemiasterlin binds in tubulin's vinca domain, in the peptide site.

The binding of radiolabeled vinca alkaloids (e.g., vinblastine, vincristine) to tubulin's vinca domain is inhibited noncompetitively by the antimitotic peptide drugs dolastatin 10, phomopsin A, and cryptophycin A. The convergence on a common, negative x-axis intercept of Hanes plots indicates that hemiasterlin is also such a noncompetitive inhibitor.

Details: Following addition of tubulin (5 µM_final) to the inhibitor (hemiasterlin) + *drug as indicated (in 0.1 M MES, pH 6.6, 5% DMSO, 0.5 mM MgCl₂), incubation proceeded 20 minutes, and [³H]drug–tubulin was resolved in duplicate samples by centrifugal gel filtration (Sephadex G-50). All at room temperature. Points are means of 3 experiments. Curves by linear regression.
 

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