Differential modulation of actin-severing activity of gelsolin by multiple isoforms of cultured rat cell tropomyosin. Potentiation of protective ability of tropomyosins by 83-kDa nonmuscle caldesmon

R. Ishikawa, S. Yamashiro, F. Matsumura

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Multiple isoforms of tropomyosin (TM) of rat cultured cells show differential effects on actin-severing activity of gelsolin. Flow birefringence measurements have revealed that tropomyosin isoforms with high M(r) values (high M(r) TMs) partially project actin filaments from fragmentation by gelsolin, while tropomyosins with low M(r) values (low M(r) TMs) have no significant protection even when the actin filaments have been fully saturated with low M(r) TMs. We have also examined effect of nonmuscle caldesmon on the severing activity of gelsolin because 83-kDa nonmuscle caldesmon stimulates actin binding of rat cell (TMs (Yamashiro-Matsumura, S., and Matsumura, F. (1988) J. Cell Biol. 106, 1973-1983). While nonmuscle caldesmon alone or low M(r) TMs alone show no significant protection against fragmentation by gelsolin, the low M(r) TMs coupled with 83-kDa protein are able to protect actin filaments. Further, high M(r) TMs together with 83-kDa protein appear to block the severing activity completely. Electron microscopic analyses of length distribution of actin filaments have confirmed the results. The average length of control actin filaments is measured as 1.46 ± 1.0 μm, and gelsolin shortens the average length to 0.084 ± 0.039 μm. Similar short average lengths are obtained when gelsolin severs actin complexed with low M(r) TMs (0.080 ± 0.045 μm) or with nonmuscle caldesmon (0.11 ± 0.072 μm) while longer average length (0.22 ± 0.18 μm) is measured in the presence of high M(r) TMs. The simultaneous addition of nonmuscle caldesmon makes the average length considerably longer, i.e. 0.61 ± 0.37 μm in the presence of low M(r) TMS and 1.57 ± 0.97 μm in the presence of high M(r) TMs. Furthermore, the actin binding of gelsolin is strongly inhibited by co-addition of high M(r) TMs and nonmuscle caldesmon. These results suggest that TM and gelsolin share the same binding site on actin molecules and that the differences in the actin affinities between TMs are related to their abilities of protection against gelsolin.

Original languageAmerican English
Pages (from-to)7490-7497
Number of pages8
JournalJournal of Biological Chemistry
Issue number13
StatePublished - 1989

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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