Design and characterization of a traceable protein kinase Calpha.
Protein kinase Calpha (PKCalpha) is a critical component of pathways that govern cancer-related phenotypes such as invasion and proliferation. Proteins that serve as immediate substrates for PKCalpha offer potential targets for anticancer drug design. To identify specific substrates, a mutant of PKCalpha (M417A) was constructed at the ATP binding site such that it could bind a sterically large ATP analogue derivatized through the N6 amino group of adenosine ([gamma-32P]-N6-phenyl-ATP). Because this analogue could be utilized by the mutant kinase but not by wild-type PKCalpha (or presumably other protein kinase) to phosphorylate peptide or protein substrates, 32P-labeled products were the direct result of the mutant PKCalpha. Kinetic analysis with [gamma-32P]-N6-phenyl-ATP revealed that the mutant retained undiminished affinity for the peptide substrate (Km = 12.4 microM) and a Vmax value (10.3 pmol/min) that was only 3-fold lower than that exhibited by the wild-type enzyme with natural ATP. However, with [gamma-32P]ATP, the mutant had a somewhat lower affinity (Km = 82.8 microM) than the wild-type enzyme (Km = 9.3 microM) in vitro but was competent in causing aggressive motility in nonmotile MCF-10A human breast cells (with endogenous ATP), as previously described for wild-type PKCalpha. The FLAG-tagged PKCalpha mutant was expressed in MCF-10A cells and used to co-immunoprecipitate high-affinity substrates from lysates. Immunopellets were reacted with [gamma-32P]-N6-phenyl-ATP, and radiolabeled products were analyzed by SDS-PAGE and autoradiography. Mass spectrometry of selected bands identified several known substrates of PKC, thereby validating the methods used in these studies. These findings provide a foundation for future applications of this traceable PKCalpha mutant.
Abeyweera
Thushara P
TP
Department of Chemistry and Biochemistry of Queens College, The City University of New York, Flushing, New York 11367-1597, USA.
Rotenberg
Susan A
SA
D000255:Adenosine Triphosphate / Q000378:metabolism; D000595:Amino Acid Sequence; D001483:Base Sequence; D002460:Cell Line; D017931:DNA Primers; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D051571:Protein Kinase C-alpha / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013379:Substrate Specificity
D017931:DNA Primers; D000255:Adenosine Triphosphate; D051571:Protein Kinase C-alpha