Gelsolin is an actin filament severing protein composed of six similar structured domains that differ with respect to actin, calcium and polyphospho-inositide binding. Previous work has established that gelsolin binds tropomyosin [Koepf, E.K. and Burtnick, L.D. (1992) FEBS Lett. 309, 56–58]. We have produced various specific gelsolin domains in Escherichia coli in order to establish which of the six domains binds tropomyosin. Gelsolin domains 1–3 (G1–3), G1–2 and G2 all bind tropomyosin in a pH and calcium insensitive manner whereas binding of G4–6 to tropomyosin was barely detectable under the conditions tested. We conclude that gelsolin binds tropomyosin via domain 2 (G2).
