Brevin and vitamin D binding protein: comparison of the effects of two serum proteins on actin assembly and disassembly

作者：Andrew Lees, John G. Haddad, Shin Lin · 发表于：Biochemistry · 年份：1984 · DOI：10.1021/bi00308a030 · 被引用次数：81 · 研究领域：Vitamin D Research Studies、Biotin and Related Studies、Cellular Mechanics and Interactions

Actin depolymerizing activity in serum can be attributed to the two proteins brevin and vitamin D binding protein (DBP). To investigate their mechanisms of action, we used a number of techniques, including procedures involving the fluorescent pyrene-labeled actin probe, to compare the interaction of the two proteins with G- and F-actin in vitro. With a fluorescence enhancement assay, we determined that brevin forms a 1:2 complex and DBP forms a 1:1 complex with pyrene-G-actin. We also found that both proteins reduce the viscosity of F-actin measured with high-shear and low-shear viscometers, with brevin effective at much lower concentrations than DBP. In polymerization experiments, brevin inhibits filament elongation at substoichiometric levels by inhibiting monomer addition at the barbed end but can also accelerate polymerization by nucleating assembly of filaments which grow from the pointed end. DBP does not nucleate filament assembly and inhibits filament elongation at either end only at near-stoichiometric levels. Brevin, but not DBP, accelerates disassembly of filaments diluted into a depolymerizing medium. This is consistent with the capability of brevin to sever preformed filaments associated with erythrocyte membranes and to increase the number of filament ends as estimated by a cytochalasin binding assay. In steady-state experiments involving the use of pyrene-actin, brevin produces only a small increase in the apparent monomer concentration when the critical concen...