title: MRI biosensor for protein kinase A encoded by a single synthetic gene.
abstract: OBJECTIVE
  Protein kinases including protein kinase A (PKA) underlie myriad important signaling pathways. The ability to monitor kinase activity in vivo and in real-time with high spatial resolution in genetically specified cellular populations is a yet unmet need, crucial for understanding complex biological systems as well as for preclinical development and screening of novel therapeutics.
  
  
  METHODS
  Using the hypothesis that the natural recognition sequences of protein kinases may be detected using chemical exchange saturation transfer magnetic resonance imaging, we designed a genetically encoded biosensor composed of eight tandem repeats of the peptide LRRASLG, a natural target of PKA.
  
  
  RESULTS
  This sensor displays a measurable change in chemical exchange saturation transfer signal following phosphorylation by PKA. The natural PKA substrate LRRASLG exhibits a chemical exchange saturation transfer-magnetic resonance imaging contrast at +1.8 and +3.6 ppm, with a >50% change after phosphorylation with minutes-scale temporal resolution. Expression of a synthetic gene encoding eight monomers of LRRASLG yielded two peaks at these chemical exchange saturation transfer frequencies.
  
  
  CONCLUSIONS
  Taken together, these results suggest that this gene may be used to assay PKA levels in a biologically relevant system. Importantly, the design strategy used for this specific sensor may be adapted for a host of clinically interesting protein kinases.
authors.affiliation: Russell H. Morgan Department of Radiology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21231, USA.
authors.forename: Raag D
authors.initials: RD
authors.lastname: Airan
authors.forename: Amnon
authors.initials: A
authors.lastname: Bar-Shir
authors.forename: Guanshu
authors.initials: G
authors.lastname: Liu
authors.forename: Galit
authors.initials: G
authors.lastname: Pelled
authors.forename: Michael T
authors.initials: MT
authors.lastname: McMahon
authors.forename: Peter C M
authors.initials: PC
authors.lastname: van Zijl
authors.forename: Jeff W M
authors.initials: JW
authors.lastname: Bulte
authors.forename: Assaf A
authors.initials: AA
authors.lastname: Gilad
mesh_terms: D015374:Biosensing Techniques / Q000379:methods*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000032:analysis* / Q000235:genetics*; D005813:Genes, Synthetic / Q000235:genetics; D008279:Magnetic Resonance Imaging / Q000379:methods*; D057054:Molecular Imaging / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
chemical_list: D017868:Cyclic AMP-Dependent Protein Kinases