GRP94 resides within cardiac sarcoplasmic reticulum vesicles and is phosphorylated by casein kinase II.
Cardiac sarcoplasmic reticulum (SR) plays a dominant role in cellular Ca2+ homeostasis by storing and releasing Ca2+. SDS-polyacrylamide gel electrophoresis and Stains All staining reveals that at least six Ca(2+)-binding proteins are contained in cardiac SR vesicles, five of which have now been identified. These five SR proteins comprise a set of high capacity Ca(2+)-binding proteins, localized to the SR lumen, that exhibit properties expected for physiological Ca2+ stores. In this study, we have purified and isolated cDNA clones for the sixth major Stains All blue-staining protein of dog cardiac SR and identified it as GRP94 (glucose-regulated protein, M(r) = 94,000). Previously, this prominent Ca(2+)-binding component has only been described in non-muscle endoplasmic reticulum. Cardiac GRP94 co-sedimented with cardiac SR vesicles and all previously described SR markers and was completely contained within the SR lumen. GRP94, like several other SR Ca(2+)-binding proteins, was a substrate for casein kinase II and was phosphorylated at two or more sites located near the two ends of the molecule. A low level of endogenous casein kinase II activity was found in crude preparations of cardiac SR but did not co-purify with SR vesicles after calcium oxalate loading, suggesting that casein kinase II phosphorylation in vivo occurs at a site other than the SR.
Cala
S E
SE
Department of Medicine, Indiana University School of Medicine, Indianapolis 46202.
Jones
L R
LR
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D047390:Casein Kinase II; D003001:Cloning, Molecular; D018076:DNA, Complementary; D004285:Dogs; D018840:HSP70 Heat-Shock Proteins; D006360:Heat-Shock Proteins / Q000378:metabolism*; D066298:In Vitro Techniques; D008565:Membrane Proteins / Q000378:metabolism*; D008969:Molecular Sequence Data; D009206:Myocardium / Q000378:metabolism*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*
D018076:DNA, Complementary; D018840:HSP70 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D008565:Membrane Proteins; C018551:glucose-regulated proteins; D047390:Casein Kinase II; D017346:Protein Serine-Threonine Kinases