Role of protein kinase CK2 phosphorylation in the molecular chaperone activity of nucleolar protein b23.
Protein B23 is a multifunctional nucleolar protein whose molecular chaperone activity is proposed to play role in ribosome assembly. Previous studies (Szebeni, A., and Olson, M. O. J. (1999) Protein Sci. 8, 905-912) showed that protein B23 has several characteristics typical of molecular chaperones, including anti-aggregation activity, promoting the renaturation of denatured proteins, and preferential binding to denatured substrates. However, until now there has been no proposed mechanism for release of a bound substrate. Protein B23 can be phosphorylated by protein kinase CK2 (CK2) in a segment required for chaperone activity. The presence of bound substrate enhanced the rate of CK2 phosphorylation of protein B23 by 2-3-fold, and this enhancement was dependent on a nonpolar region in its N-terminal end. Formation of a complex between B23 and chaperone test substrates (rhodanese or citrate synthase) was inhibited by CK2 phosphorylation. Furthermore, CK2 phosphorylation of a previously formed B23-substrate complex promoted its dissociation. The dissociation of complexes between B23 and the human immunodeficiency virus-Rev protein required both CK2 phosphorylation and competition with a Rev nuclear localization signal peptide, suggesting that Rev binds B23 at two separate sites. These studies suggest that unlike many molecular chaperones, which directly hydrolyze ATP, substrate release by protein B23 is dependent on its phosphorylation by CK2.
Szebeni
Attila
A
Department of Biochemistry, University of Mississippi Medical Center, Jackson, Mississippi 39216, USA.
Hingorani
Kamini
K
Negi
Sandeep
S
Olson
Mark O J
MO
D000818:Animals; D047390:Casein Kinase II; D002467:Cell Nucleus / Q000378:metabolism*; D004926:Escherichia coli / Q000378:metabolism; D015694:Gene Products, rev / Q000378:metabolism; D006801:Humans; D006868:Hydrolysis; D008954:Models, Biological; D009154:Mutation; D009687:Nuclear Proteins / Q000737:chemistry*; D000090243:Nucleophosmin; D010455:Peptides / Q000737:chemistry; D010748:Phosphopeptides / Q000737:chemistry; D010766:Phosphorylation; D011485:Protein Binding; D011489:Protein Denaturation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D051381:Rats; D011994:Recombinant Proteins / Q000737:chemistry; D013997:Time Factors
D015694:Gene Products, rev; D009687:Nuclear Proteins; D010455:Peptides; D010748:Phosphopeptides; D011994:Recombinant Proteins; D000090243:Nucleophosmin; D047390:Casein Kinase II; D017346:Protein Serine-Threonine Kinases