Langer M, Giebing T, D'Haese J
Institut für Zoomorphologie, Zellbiologie und Parasitologie, Heinrich-Heine-Universität, Düsseldorf, Germany.
Comp Biochem Physiol B Biochem Mol Biol. 1998 Apr;119(4):697-704. doi: 10.1016/s0305-0491(98)00045-5.
From the pharyngeal baskets of the ascidians Microcosmus sulcatus and Phallusia mammilata we have purified an 85-kDa protein that is characterized as a member of the gelsolin family. These proteins from both species show the same behaviour in functional assays. The ascidian gelsolin binds two actin monomers in a highly cooperative manner. This complex formation is Ca(2+)-dependent, but not completely reversible, as on removal of Ca2+ one actin monomer dissociates leaving a 1:1 complex between gelsolin and G-actin. The properties of F-actin severing and G-actin nucleation depend on the presence of free Ca2+ in a micromolar range, with half maximum activation at about 3 x 10(-6) M. The protein becomes inactivated when Ca2+ concentrations of 0.5 mM are exceeded. Fragmentation of F-actin by the ascidian gelsolin is comparably fast to that of vertebrate gelsolin. A steady state of actin fragmentation is reached within 2-4 s. Promotion of G-actin nucleation is also comparable to that of vertebrate gelsolin. Regarding functional aspects, the ascidian gelsolin is more closely related to vertebrate gelsolin than to an arthropod gelsolin from crayfish tail muscle.
从海鞘Microcosmus sulcatus和Phallusia mammilata的咽篮中，我们纯化出了一种85 kDa的蛋白质，其被鉴定为凝溶胶蛋白家族的成员。来自这两个物种的这些蛋白质在功能测定中表现出相同的行为。海鞘凝溶胶蛋白以高度协同的方式结合两个肌动蛋白单体。这种复合物的形成依赖于Ca(2+)，但不是完全可逆的，因为去除Ca2+后，一个肌动蛋白单体会解离，在凝溶胶蛋白和G-肌动蛋白之间留下1:1的复合物。F-肌动蛋白切断和G-肌动蛋白成核的特性取决于微摩尔范围内游离Ca2+的存在，在约3×10(-6) M时达到最大激活的一半。当Ca2+浓度超过0.5 mM时，该蛋白质会失活。海鞘凝溶胶蛋白对F-肌动蛋白的切割速度与脊椎动物凝溶胶蛋白相当。在2-4秒内达到肌动蛋白切割的稳态。G-肌动蛋白成核的促进作用也与脊椎动物凝溶胶蛋白相当。在功能方面，海鞘凝溶胶蛋白与脊椎动物凝溶胶蛋白的关系比与小龙虾尾肌中的节肢动物凝溶胶蛋白更为密切。
