Purification, amino-terminal sequence and functional properties of a 64 kDa cytosolic protein from heart muscle capable of modulating calcium transport across the sarcoplasmic reticulum in vitro

Protective immunity induced in mice by F8.1 and F8.2 antigens purified from Schistosoma mansoni eggs

Schistosoma mansoni soluble egg antigens (SEA) were fractionated by isoelectric focusing, resulting in 20 components, characterized by pH, absorbance and protein concentration. The higher absorbance fractions were submitted to electrophoresis, and fraction 8 (F8) presented a specific pattern of bands on its isoelectric point. Protein 3 was observed only on F8, and so, it was utilized to rabbit immunization, in order to evaluate its capacity of inducing protective immunity. IgG antibodies from rabbit anti-F8 serum were coupled to Sepharose, and used to obtain the specific antigen by affinity chromatography. This antigen, submitted to electrophoresis, presented two proteic bands (F8.1 and F8.2), which were transferred to nitrocellulose membrane (PVDF) and sequenciated. The homology of F8.2 to known proteins was determined using the Basic Local Alignment Search Tool program (BLASTp). Significant homologies were obtained for the rabbit cytosolic Ca2+ uptake inhibitor, and for the bird a1-proteinase inhibitor. Immunization of mice with F8.1 and F8.2, in the presence of Corynebacterium parvum and Al(OH)3 as adjuvant, induced a significant protection degree against challenge infection, as observed by the decrease on worm burden recovered from portal system.

Phosphorylation and regulation of the Ca(2+)-pumping ATPase in cardiac sarcoplasmic reticulum by calcium/calmodulin-dependent protein kinase

In cardiac muscle, a membrane-associated Ca2+/calmodulin-dependent protein kinase (CaM kinase) phosphorylates the Ca(2+)-pumping ATPase in addition to its previously characterized substrates, phospholamban and Ca(2+)-release channel (ryanodine receptor). The phosphorylated amino acid in the Ca(2+)-ATPase has been identified as serine. Posphorylation of the Ca(2+)-ATPase is rapid and is reversible by a membrane-associated protein phosphatase, Ca(2+)-ATPase purified from cardiac SR underwent phosphorylation by exogenous CaM kinase, and the phosphorylated enzyme displayed twofold greater catalytic activity without alteration in its Ca(2+)-sensitivity. The phosphorylation of the Ca(2+)-ATPase was found to be isoform-specific in that the cardiac and slow-twitch skeletal muscle isoform (SERCA 2), but not the fast-twitch skeletal muscle isoform (SERCA 1), underwent phosphorylation by CaM kinase. Studies using SERCA 1 and SERCA 2 isoforms and their mutants expressed in a heterelogous cell system have resulted in i) confirmation of the isoform specificity of Ca(2+)-ATPase phosphorylation by CaM kinase, ii) identification of Ser38 as the site in SERCA 2 phosphorylated by CaM kinase, and iii) demonstration of phosphorylation-induced increase in Vmax of Ca2+ transport by the SERCA 2 enzyme. These observations suggest that in cardiac and slow-twitch skeletal muscle direct phosphorylation of the SR Ca(2+)-ATPase by the membrane-bound CaM kinase may serve to stimulate Ca2+ sequestration and therefore, the speed of muscle relaxation.