Interaction of thiabendazole with fungal tubulin

Thiabendazole, 2-(4'-thiazolyl)benzimidazole, at 80 micrometer completely inhibits mitosis in hyphae of Aspergillus nidulans, growing in liquid culture. DNA and RNA synthesis and mycelial growth are only partially inhibited at this concentration. Binding studies with cell-free mycelial extracts from Penicillium expansum showed that thiabendazole competitively inhibits [14C]carbendazim binding to tubulin, which suggests that the antimitotic activity of thiabendazole is based on interference with microtubule assembly. Tubulin from a thiabendazole-resistant and carbendazim-highly sensitive mutant of P. expansum has a lower affinity to thiabendazole and a higher affinity to carbendazim than tubulin from a wide-type strain. This indicates that in this mutant the structure of the binding site is affected. The data presented suggest that several sites of both the tubulin and ligand molecule are involved in the binding of benzimidazole compounds to fungal tubulin.