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  • Title: Endoplasmic reticulum stress-inducible protein GRP94 is associated with an Mg2+-dependent serine kinase activity modulated by Ca2+ and GRP78/BiP.
    Author: Ramakrishnan M, Schönthal AH, Lee AS.
    Journal: J Cell Physiol; 1997 Feb; 170(2):115-29. PubMed ID: 9009140.
    Abstract:
    The 94-kDa glucose-regulated protein (GRP94) is a glycoprotein in the endoplasmic reticulum (ER). It has been characterized as a Ca2+-binding protein and a molecular chaperone. In this report we show that highly purified GRP94 exhibits an active Mg2+-dependent serine kinase activity (termed 94-kinase). The 94-kinase can be recovered from ER membrane fractions and is able to phosphorylate both the constitutive and stress-induced forms of GRP94, correlating with their induction kinetics. The 94-kinase activity is distinct from casein kinase II. In contrast to the heat-stable, Ca2+-dependent autophosphorylation activity recently reported for GRP94, the labile 94-kinase activity is inhibited by Ca2+. We determined that the phosphopeptide map of in vitro phosphorylated GRP94 by the 94-kinase resembles that of the in vivo phosphorylated GRP94. Further, the 94-kinase activity can be specifically stimulated by GRP78, a coregulated protein in the ER known to interact with GRP94.
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