fimbrin belongs to the calponin homology (ch) domain superfamily of actin cross-linking proteins. like other members of this superfamily, which include α-actinin, β-spectrin, dystrophin, abp-120 and filamin, it has a conserved 27 kda actin-binding domain that contains a tandem duplication of a sequence that is homologous to calponin. in addition to cross-linking actin filaments into bundles and networks, ch domains also bind intermediate filaments and some signal transduction proteins to the actin cytoskeleton. structural comparison of actin filaments and fimbrin ch domain-decorated actin filaments has revealed changes in the actin structure due to fimbrin-mediated cross-linking that may affect the actin filaments' affinity for other actin-binding proteins and may be part of the regulation of the cytoskeleton itself.