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Effects of inhibitors of tubulin polymerization on GTP hydrolysis
Abstract:
The effects of a number of antimitotic drugs on the GTPase activity of tubulin were examined. The previously reported stimulation with colchicine and inhibition with podophyllotoxin and vinblastine wee confirmed. Maytansine, which competes with vinblastine in binding to tubulin, was comparable to the latter in inhibiting GTP hydrolysis. Nocodazole, which competes with colchicine in binding to tubulin, was significantly superior to colchicine in enhancing GTP hydrolysis. This superiority arose from the more rapid bindng of nocodazole to tubulin, as the two drugs had comparable activity when drug and tubulin were preincubated prior to the addition of GTP. Both colchicine and podophyllotoxin contain a trimethoxybenzene ring, while the closest structural analogy of nocodazole to colchicine includes the trimethoxybenzene ring. To explore this apparent paradox, we examined a number of simpler colchicine analogs for their effects on tubulin-dependent GTP hydrolysis. While tropolone was without effect, 3,4,5-trimethoxybenzaldehyde and 2,3,4-trimethoxybenzaldehyde stimulated the reaction. We therefore conclude that the trimethoxybenzene ring of colchicine is primarily responsible for the drug's stimulation of the GTPase activity of tubulin and that the inhibitory effect of podophyllotoxin must derive from the latter's tetrahydronaphthol moiety.
Insights
Antimitotic drugs affect tubulin's GTPase activity. The trimethoxybenzene ring in drugs like colchicine stimulates this activity, while other parts of the molecules cause inhibition.
Area of Science:
- Biochemistry
- Molecular Biology
- Pharmacology
Background:
- Antimitotic drugs disrupt microtubule dynamics, crucial for cell division.
- Tubulin GTPase activity is a key target for these drugs.
- Previous studies indicated varied effects of drugs on tubulin GTPase activity.
Purpose of the Study:
- To investigate the impact of various antimitotic drugs on tubulin's GTPase activity.
- To elucidate the structural components of these drugs responsible for their effects on tubulin.
Main Methods:
- Assay of tubulin GTPase activity in the presence of different antimitotic drugs.
- Comparison of drug binding kinetics and GTP hydrolysis.
- Examination of simpler drug analogs to identify key structural motifs.
Main Results:
- Colchicine and nocodazole stimulated GTP hydrolysis, while podophyllotoxin and vinblastine inhibited it.
- Nocodazole showed superior stimulation compared to colchicine due to faster binding.
- Trimethoxybenzene-containing analogs stimulated GTP hydrolysis, implicating this moiety in colchicine's effect.
Conclusions:
- The trimethoxybenzene ring is primarily responsible for stimulating tubulin GTPase activity, as seen with colchicine.
- The inhibitory effects of podophyllotoxin are attributed to its tetrahydronaphthol moiety.
- Drug-tubulin binding kinetics significantly influence the observed GTPase activity modulation.