unique properties of eukaryote-type actin and profilin horizontally transferred to cyanobacteria独特的eukaryote-type肌动蛋白的性质和profilin水平转移到蓝藻.pdf

Unique Properties of Eukaryote-Type Actin and Profilin Horizontally Transferred to Cyanobacteria 1 2 3 ¨ 2 1 Arthur Guljamow *, Friedmar Delissen , Otto Baumann , Andreas F. Thunemann , Elke Dittmann ¨ ¨ 1 University Potsdam, Institute for Biochemistry and Biology, Department of Microbiology, Golm, Germany, 2 Bundesanstalt fur Materialforschung und -prufung Federal Institute for Materials Research and Testing, Berlin, Germany, 3 University Potsdam, Institute for Biochemistry and Biology, Department of Animal Physiology, Golm, Germany Abstract A eukaryote-type actin and its binding protein profilin encoded on a genomic island in the cyanobacterium Microcystis aeruginosa PCC 7806 co-localize to form a hollow, spherical enclosure occupying a considerable intracellular space as shown by in vivo fluorescence microscopy. Biochemical and biophysical characterization reveals key differences between these proteins and their eukaryotic homologs. Small-angle X-ray scattering shows that the actin assembles into elongated, filamentous polymers which can be visualized microscopically with fluorescent phalloidin. Whereas rabbit actin forms thin cylindrical filaments about 100 mm in length, cyanobacterial actin polymers resemble a ribbon, arrest polymerization at 5- 10 mm and tend to form irregular multi-strand assemblies. While eukaryotic profilin is a specific actin monomer binding protein, cyanobacterial profilin shows the unprecedented property of decorating actin filaments. Electron micrographs show that cyanobacterial p