title: Site-Specific Labeling of Protein Kinase CK2: Combining Surface Display and Click Chemistry for Drug Discovery Applications.
abstract: Human CK2 is a heterotetrameric constitutively active serine/threonine protein kinase and is an emerging target in current anti-cancer drug discovery. The kinase is composed of two catalytic CK2α subunits and two regulatory CK2β subunits. In order to establish an assay to identify protein-protein-interaction inhibitors (PPI) of the CK2α/CK2β interface, a bioorthogonal click reaction was used to modify the protein kinase α-subunit with a fluorophore. By expanding the genetic code, the unnatural amino acid para azidophenylalanine (pAzF) could be incorporated into CK2α. Performing the SPAAC click reaction (Strain-Promoted Azide-Alkyne Cycloaddition) by the use of a dibenzylcyclooctyne-fluorophore (DBCO-fluorophore) led to a specifically labeled human protein kinase CK2α. This site-specific labeling does not impair the phosphorylation activity of CK2, which was evaluated by capillary electrophoresis. Furthermore a dissociation constant (KD) of 631 ± 86.2 nM was determined for the substrate αS1-casein towards CK2α. This labeling strategy was also applied to CK2β subunit on Escherichia coli, indicating the site-specific modifications of proteins on the bacterial cell surface when displayed by Autodisplay.
authors.affiliation: Institut f&#252;r Pharmazeutische und Medizinische Chemie, PharmaCampus, Westf&#228;lische Wilhelms-Universit&#228;t M&#252;nster, Corrensstraße 48, D-48149 M&#252;nster, Germany. christian.nienberg@uni-muenster.de.
authors.forename: Christian
authors.initials: C
authors.lastname: Nienberg
authors.affiliation: Institut f&#252;r Pharmazeutische und Medizinische Chemie, PharmaCampus, Westf&#228;lische Wilhelms-Universit&#228;t M&#252;nster, Corrensstraße 48, D-48149 M&#252;nster, Germany. a_rett04@uni-muenster.de.
authors.forename: Anika
authors.initials: A
authors.lastname: Retterath
authors.affiliation: Institut f&#252;r Biochemie, Westf&#228;lische Wilhelms-Universit&#228;t M&#252;nster, Wilhelm-Klemm-Straße 2, D-48149 M&#252;nster, Germany. kira.becher@uni-muenster.de.
authors.forename: Kira-Sophie
authors.initials: KS
authors.lastname: Becher
authors.affiliation: Institut f&#252;r Pharmazeutische und Medizinische Chemie, PharmaCampus, Westf&#228;lische Wilhelms-Universit&#228;t M&#252;nster, Corrensstraße 48, D-48149 M&#252;nster, Germany. thorsten.saenger@uni-muenster.de.
authors.forename: Thorsten
authors.initials: T
authors.lastname: Saenger
authors.affiliation: Institut f&#252;r Biochemie, Westf&#228;lische Wilhelms-Universit&#228;t M&#252;nster, Wilhelm-Klemm-Straße 2, D-48149 M&#252;nster, Germany. henning.mootz@uni-muenster.de.
authors.forename: Henning D
authors.initials: HD
authors.lastname: Mootz
authors.affiliation: Institut f&#252;r Pharmazeutische und Medizinische Chemie, PharmaCampus, Westf&#228;lische Wilhelms-Universit&#228;t M&#252;nster, Corrensstraße 48, D-48149 M&#252;nster, Germany. joachim.jose@uni-muenster.de.
authors.forename: Joachim
authors.initials: J
authors.lastname: Jose
keywords: Autodisplay; CK2; bioorthogonal; click chemistry; drug discovery; kinase; labeling; protein-protein interaction; unnatural amino acid