An Arabidopsis Calcium-Dependent Protein Kinase Is Associated with the Endoplasmic Reticulum

• Published in: Plant physiology (Bethesda) Vol. 128; no. 3; pp. 1008 - 1021
• Main Authors: LU, Sheen X, HRABAK, Estelle M
• Format: Journal Article
• Language: English
• Published: Rockville, MD American Society of Plant Biologists 01.03.2002; American Society of Plant Physiologists
• Subjects: Amino acids; Animals; Antibodies; Arabidopsis; Arabidopsis - enzymology; Arabidopsis - genetics; Arabidopsis Proteins - genetics; Arabidopsis Proteins - metabolism; AtCPK2 gene; Biological and medical sciences; Calcium; Calcium - metabolism; Calcium-Binding Proteins - genetics; Calcium-Binding Proteins - metabolism; Cell biochemistry; Cell Biology and Signal Transduction; Cell membranes; Cell physiology; Cloning, Molecular; DNA, Plant - chemistry; DNA, Plant - genetics; Endoplasmic Reticulum - enzymology; Female; Fundamental and applied biological sciences. Psychology; Gene Expression Regulation, Enzymologic; Gene Expression Regulation, Plant; Genetic mutation; Genomics; Glucuronidase - genetics; Glucuronidase - metabolism; Membrane Proteins - genetics; Membrane Proteins - metabolism; Molecular Sequence Data; Mutation; Myristic Acid - metabolism; myristoylation; Plant cells; Plant physiology and development; Plant Proteins; Plants; Plants, Genetically Modified; Protein Kinases - genetics; Protein Kinases - metabolism; protein trafficking; Proteins; Rabbits; Recombinant Fusion Proteins - genetics; Recombinant Fusion Proteins - metabolism; Sequence Analysis, DNA; Transgenic plants; Cell compartment; Leader peptide; Membrane protein; Calcium; Targeting; Enzyme; Transferases; Biomembrane; Myristoylation; Arabidopsis thaliana; Cruciferae; Protein kinase; Dicotyledones; Angiospermae; Spermatophyta; Property structure relationship; Mutation; Experimental plant; Localization; Endoplasmic reticulum
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.010770

Arabidopsis contains 34 genes that are predicted to encode calcium-dependent protein kinases (CDPKs). CDPK enzymatic activity previously has been detected in many locations in plant cells, including the cytosol, the cytoskeleton, and the membrane fraction. However, little is known about the subcellular locations of individual CDPKs or the mechanisms involved in targeting them to those locations. We investigated the subcellular location of one Arabidopsis CDPK, AtCPK2, in detail. Membrane-associated AtCPK2 did not partition with the plasma membrane in a two-phase system. Sucrose gradient fractionation of microsomes demonstrated that AtCPK2 was associated with the endoplasmic reticulum (ER). AtCPK2 does not contain transmembrane domains or known ER-targeting signals, but does have predicted amino-terminal acylation sites. AtCPK2 was myristoylated in a cell-free extract and myristoylation was prevented by converting the glycine at the proposed site of myristate attachment to alanine (G2A). In plants, the G2A mutation decreased AtCPK2 membrane association by approximately 50%. A recombinant protein, consisting of the first 10 amino acids of AtCPK2 fused to the amino-terminus of β-glucuronidase, was also targeted to the ER, indicating that the amino terminus of AtCPK2 can specify ER localization of a soluble protein. These results indicate that AtCPK2 is localized to the ER, that myristoylation is likely to be involved in the membrane association of AtCPK2, and that the amino terminal region of AtCPK2 is sufficient for correct membrane targeting.