Phosphorylation by actin kinase of the pointed end domain on the actin molecule.
Fragmin from plasmodium of Physarum polycephalum binds G-actin and severs F-actin in the presence of Ca2+ over 10(-6) M. The fragmin-actin complex consisting of fragmin and G-actin nucleates actin polymerization and caps the barbed (fast growing) end of F-actin, regardless of the concentrations of Ca2+, and the actin filaments are shortened. Actin kinase purified from plasmodium abolishes the nucleation and capping activities of the complex by phosphorylating actin of the fragmin-actin complex (Furuhashi, K., and Hatano, S. (1990) J. Cell. Biol. 111, 1081-1087). This inactivation of the complex leads to production of long actin filaments. We obtained evidence that Physarum actin is phosphorylated by actin kinase at Thr-201, and probably at Thr-202 and/or Thr-203, with 1 mol of phosphate distributed among them. This finding raises the possibility that the site of phosphorylation, Thr-201 to Thr-203, is positioned on the pointed (slow growing) end domain of the actin molecule, because growth of actin filaments from the fragmin-actin complex occurs only from the pointed end. These observations are consistent with a model of the three-dimensional structure of G-actin. Inactivation of the fragmen-actin complex may follow phosphorylation of the pointed end domain of actin.
Furuhashi
K
K
Department of Molecular Biology, School of Science, Nagoya University, Japan.
Hatano
S
S
Ando
S
S
Nishizawa
K
K
Inagaki
M
M
D000199:Actins / Q000737:chemistry / Q000378:metabolism*; D000596:Amino Acids / Q000032:analysis; D000818:Animals; D002851:Chromatography, High Pressure Liquid; D004591:Electrophoresis, Polyacrylamide Gel; D006495:Heparin, Low-Molecular-Weight / Q000378:metabolism; D010449:Peptide Mapping; D010766:Phosphorylation; D010804:Physarum / Q000378:metabolism; D011487:Protein Conformation; D011494:Protein Kinases / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases; D013379:Substrate Specificity; D014357:Trypsin / Q000378:metabolism
D000199:Actins; D000596:Amino Acids; D006495:Heparin, Low-Molecular-Weight; D011494:Protein Kinases; C074377:actin kinase; D017346:Protein Serine-Threonine Kinases; D014357:Trypsin