Rl. Bai et al., Interactions of the sponge-derived antimitotic tripeptide hemiasterlin with tubulin: Comparison with dolastatin 10 and cryptophycin 1, BIOCHEM, 38(43), 1999, pp. 14302-14310
The sponge-derived antimitotic tripeptide hemiasterlin was previously shown
to inhibit tubulin polymerization. We have now demonstrated that hemiaster
lin resembles most other antimitotic peptides in noncompetitively inhibitin
g the binding of vinblastine to tubulin (apparent K-i value, 7.0 mu M), com
petitively inhibiting the binding of dolastatin 10 to tubulin (apparent K-i
value, 2.0 mu M), stabilizing the colchicine binding activity of tubulin,
inhibiting nucleotide exchange on beta-tubulin, and inducing the formation
of tubulin oligomers that are stable to gel filtration in the absence of fr
ee drug, even at low drug concentrations. The tubulin oligomerization react
ion induced by hemiasterlin was compared to the reactions induced by dolast
atin 10 and cryptophycin 1. Like dolastatin 10, hemiasterlin induced format
ion of a tubulin aggregate that had the morphological appearance primarily
of ring-like structures with a diameter of about 40 nm, while the morpholog
y of the cryptophycin 1 aggregate consisted primarily of smaller rings (dia
meter about 30 nm). However, the hemiasterlin aggregate differed from the d
olastatin 10 aggregate in that its formation was not associated with turbid
ity development, and the morphology of the hemiasterlin aggregate (as oppos
ed to the dolastatin 10 aggregate) did not change greatly when microtubule-
associated proteins were present (tight coils and pinwheels are observed wi
th dolastatin 10 but not with hemiasterlin or cryptophycin 1). Opacificatio
n of tubulin-dolastatin 10 mixtures was inhibited by hemiasterlin at 22 deg
rees C and stimulated at 0 degrees C, while cryptophycin 1 was inhibitory a
t both reaction temperatures.