Interactions of plasma gelsolin with actin. Isolation and characterization of binary and ternary plasma-gelsolin-actin complexes.
We have studied the interactions between plasma gelsolin and actin: firstly the complex formation between both proteins, secondly the effects of gelsolin and its complexes on G-actin polymerization and F-actin fragmentation. Complex formation has been studied by high-performance gel permeation chromatography; plasma gelsolin alone elutes at an Mr of about 77000 and a Stokes radius of 3.7 nm; complex formation occurs in the presence of Ca2+: by chromatography in the presence of EGTA, a binary complex is obtained with an Mr of 134000 and a Stokes radius of 4.7 nm; and by chromatography in the presence of Ca2+, a ternary complex is obtained with an Mr of 173000 and a Stokes radius of 5.2 nm. The binary complex is EGTA-stable. In relation to this stability of the binary complex, the depolymerizing function of gelsolin is not reversed upon chelation of Ca2+. The effects of plasma gelsolin and its complexes on both G-actin polymerization and F-actin fragmentation, and their Ca2+ dependence have been examined by viscometry and electron microscopy. The main conclusions of these studies are the following: the fast processes are the formation of ternary complex, which acts as a heteronucleus for G-actin polymerization, and the severing function of gelsolin, these fast processes are Ca2+-dependent; the slow processes are related to the capping ability of gelsolin or its complexes and are Ca2+-independent.
D000199:Actins / Q000097:blood* / Q000302:isolation & purification; D001704:Biopolymers; D002118:Calcium / Q000494:pharmacology; D002135:Calcium-Binding Proteins / Q000097:blood* / Q000302:isolation & purification; D002850:Chromatography, Gel / Q000379:methods; D018260:Gelsolin; D006801:Humans; D008840:Microfilament Proteins / Q000097:blood* / Q000302:isolation & purification; D008854:Microscopy, Electron; D011485:Protein Binding; D014783:Viscosity
D000199:Actins; D001704:Biopolymers; D002135:Calcium-Binding Proteins; D018260:Gelsolin; D008840:Microfilament Proteins; D002118:Calcium