Shuichi Takeda, Ikuko Fujiwara, Yasunobu Sugimoto, Toshiro Oda, Akihiro Narita, Yuichiro Maéda
Journal of muscle research and cell motility 2020 MarGelsolin superfamily proteins, consisting of multiple domains (usually six), sever actin filaments and cap the barbed ends in a Ca2+-dependent manner. Two types of evolutionally conserved Ca2+-binding sites have been identified in this family; type-1 (between gelsolin and actin) and type-2 (within the gelsolin domain). Fragmin, a member in the slime mold Physarum polycephalum, consists of three domains (F1-F3) that are highly similar to the N-terminal half of mammalian gelsolin (G1-G3). Despite their similarities, the two proteins exhibit a significant difference in the Ca2+ dependency; F1-F3 absolutely requires Ca2+ for the filament severing whereas G1-G3 does not. In this study, we examined the strong dependency of fragmin on Ca2+ using biochemical and structural approaches. Our co-sedimentation assay demonstrated that Ca2+ significantly enhanced the binding of F2-F3 to actin. We determined the crystal structure of F2-F3 in the presence of Ca2+. F2-F3 binds a total of three calcium ions; while two are located in type-2 sites within F2 or F3, the remaining one resides between the F2 long helix and the F3 short helix. The inter-domain Ca2+-coordination appears to stabilize F2-F3 in a closely packed configuration. Notably, the F3 long helix exhibits a bent conformation which is different from the straight G3 long helix in the presence of Ca2+. Our results provide the first structural evidence for the existence of an unconventional Ca2+-binding site in the gelsolin superfamily proteins.
Shuichi Takeda, Ikuko Fujiwara, Yasunobu Sugimoto, Toshiro Oda, Akihiro Narita, Yuichiro Maéda. Novel inter-domain Ca2+-binding site in the gelsolin superfamily protein fragmin. Journal of muscle research and cell motility. 2020 Mar;41(1):153-162
PMID: 31863323
View Full Text