The ER-membrane-resident Hsp40 ERj1 is a novel substrate for protein kinase CK2.
The endoplasmic reticulum (ER) membrane protein ERj1, a member of the Hsp40 family, was proposed to be a regulator of protein biogenesis at the ER. With its lumenal J-domain, ERj1 recruits the lumenal Hsp70-type chaperone BiP to newly synthesized polypeptide chains. Its cytosolic domain interacts with ribosomes and inhibits protein synthesis in its BiP-free state. Additionally, the cytosolic domain may act as a transcription factor. Recent proteomic data suggest that ERj1 is a target of phosphorylation. Since protein kinase CK2 is present on the ER surface, we addressed the question whether ERj1 is a substrate for CK2. We show that native ERj1 is phosphorylated by CK2. Using deletion mutants, ERj1 peptides, and a mutational analysis, the major phosphorylation site for CK2 was mapped to the conserved sequence motif SSDEE at amino acid residues 477-481, which is located in the cytosolic domain of ERj1.
Götz
Claudia
C
Medizinische Biochemie und Molekularbiologie, Universität des Saarlandes, 66421 Homburg, Germany.
Müller
Anika
A
Montenarh
Mathias
M
Zimmermann
Richard
R
Dudek
Johanna
J
D000595:Amino Acid Sequence; D000818:Animals; D047390:Casein Kinase II / Q000378:metabolism*; D004252:DNA Mutational Analysis; D004285:Dogs; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D050956:HSP40 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008969:Molecular Sequence Data; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D017384:Sequence Deletion; D013379:Substrate Specificity
C092319:Dnajc1 protein, mouse; D050956:HSP40 Heat-Shock Proteins; D009363:Neoplasm Proteins; D047390:Casein Kinase II