Related Experiment Videos
Mapping the residues of protein kinase CK2 implicated in substrate recognition: mutagenesis of conserved basic
S Sarno1, B Boldyreff, O Marin
1Dipartimento di Chimica Biologica, CRIBI, Università di Padova, Italy.
Abstract:
Six mutants of protein kinase CK2 alpha subunit in which basic residues have been mutated into alanines were assayed for their capability to phosphorylate the peptide RRRADDSDDDDD. Two mutants (R228A and R278K279R280A) behaved more or less as alpha wild type and one (H160,166A) was nearly inactive, hampering the calculation of kinetic parameters. In contrast 3 mutants (K74-77A, K79R80K83A and R191,195K198A) phosphorylated the peptide with reduced efficiency accounted for by increased Km and decreased Vmax values. By using derivatives of the RRRADDSDDDDD peptide in which individual aspartyl residues were variably replaced by alanine(s) and two peptide substrates derived from I-2 (KYRIREQESSGEEDSDL and RRKDLHDDEEDEEMSETADGE) it was shown that mutations in the 191-198, 74-77 and 79-83 regions were the least detrimental whenever the acidic determinants were lacking at positions +1, +4/+5 and +3, respectively. These data support the conclusion that the basic residues present in the p+1 loop of CK2 alpha specifically recognize the acidic determinant adjacent to the C-terminal side of serine, while the specificity determinants located more down-stream are variably recognized by different residues of the unique basic cluster spanning between Lys74 and Lys83.
Insights
Protein kinase CK2 alpha subunit mutations reveal basic residues are crucial for substrate recognition. Specific basic residues in the p+1 loop recognize acidic determinants, influencing enzyme activity and substrate specificity.
Area of Science:
- Biochemistry
- Molecular Biology
- Enzymology
Background:
- Protein kinase CK2 (CK2) is a crucial enzyme involved in various cellular processes.
- The alpha subunit of CK2 plays a key role in substrate recognition and catalytic activity.
- Understanding the role of specific amino acid residues in CK2's function is essential for deciphering its regulatory mechanisms.
Purpose of the Study:
- To investigate the role of basic residues in the CK2 alpha subunit's catalytic activity.
- To determine how mutations in basic residues affect the phosphorylation of specific peptide substrates.
- To elucidate the contribution of different regions of the CK2 alpha subunit to substrate specificity.
Main Methods:
- Site-directed mutagenesis was used to generate six mutants of the CK2 alpha subunit, replacing basic residues with alanines.
- Enzyme kinetics assays were performed to measure the phosphorylation efficiency of wild-type and mutant CK2 alpha on various peptide substrates.
- Peptide substrates with modified acidic determinants were synthesized to probe substrate-binding interactions.
Main Results:
- Mutations in specific regions (K74-77A, K79R80K83A, R191,195K198A) significantly reduced CK2 alpha's phosphorylation efficiency, characterized by increased Km and decreased Vmax.
- A mutant (H160,166A) exhibited near-inactive phosphorylation, hindering kinetic analysis.
- Mutations were least detrimental when acidic determinants were absent at specific positions (+1, +4/+5, +3) on the peptide substrate.
Conclusions:
- Basic residues in the p+1 loop of CK2 alpha are critical for specifically recognizing the acidic determinant adjacent to the C-terminal side of serine.
- The unique basic cluster spanning Lys74 to Lys83 variably recognizes downstream specificity determinants.
- These findings provide insights into the molecular basis of CK2 alpha substrate specificity and catalytic mechanism.