RESUMEN
Chara myosin in green algae, Chara corallina, is the fastest myosin of all those observed so far. To shed light on the molecular mechanism of this fast sliding, we determined the primary structure of Chara myosin heavy chain (hc). It has a motor domain, six IQ motifs for calmodulin binding, a coiled-coil structure to dimerize, and a globular tail. Chara myosin hc is very similar to some plant myosins and has been predicted to belong to the class XI. Short loop 1 and loop 2 may account for the characteristics of mechanochemical properties of Chara myosin.
Asunto(s)
Chlorophyta/química , Corriente Citoplasmática , Proteínas Motoras Moleculares/química , Cadenas Pesadas de Miosina/química , Secuencia de Aminoácidos , Compartimento Celular , Chlorophyta/ultraestructura , Técnica del Anticuerpo Fluorescente , Biblioteca de Genes , Proteínas Motoras Moleculares/ultraestructura , Datos de Secuencia Molecular , Cadenas Pesadas de Miosina/ultraestructura , Fragmentos de Péptidos/química , Estructura Terciaria de Proteína , Análisis de Secuencia de ADN , Análisis de Secuencia de Proteína , Homología de Secuencia de Aminoácido , Factores de TiempoRESUMEN
The extracellular domain of human c-Mpl, the receptor for thrombopoietin (TPO), was expressed as a chimeric protein with the interleukin-2 receptor alpha chain on the surface of murine B cell-line B300-19. BALB/c mice were immunized with cells expressing the chimeric protein. The IgG purified from the resulting immune serum immunoprecipitated human c-Mpl. The immune IgG supported proliferation of both stable transfectant Ba/F3 cells expressing whole c-Mpl molecules (c-Mpl-Ba/F3 No. 9) and UT7/TPO cells bearing naturally occurring c-Mpl, whereas it did not support the growth of the untransfected parental Ba/F3 cells. Cell growth was induced using 3 to 100 microg/ml of immune IgG in a dose-dependent manner, but this induction was decreased at doses higher than 100 microg/ml. Non-immune IgG did not affect cell growth of c-Mpl-Ba/F3 No. 9 cells. Although the Fab fragment of immune IgG also immunoprecipitated c-Mpl, it did not support cell growth at concentrations as high as 180 microg/ml, implying that the bivalent binding of receptors by antibodies is essential for cell proliferation. These results suggest that antibodies against human c-Mpl stimulate the proliferation and differentiation of megakaryocytes by their bivalent binding to receptors like TPO.