Sensing pH via p-cyanophenylalanine fluorescence: Application to determine peptide pKa and membrane penetration kinetics.
We expand the spectroscopic utility of a well-known infrared and fluorescence probe, p-cyanophenylalanine, by showing that it can also serve as a pH sensor. This new application is based on the notion that the fluorescence quantum yield of this unnatural amino acid, when placed at or near the N-terminal end of a polypeptide, depends on the protonation status of the N-terminal amino group of the peptide. Using this pH sensor, we are able to determine the N-terminal pKa values of nine tripeptides and also the membrane penetration kinetics of a cell-penetrating peptide. Taken together, these examples demonstrate the applicability of using this unnatural amino acid fluorophore to study pH-dependent biological processes or events that accompany a pH change.
Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104, USA.
Ileana M
IM
Pazos
Department of Biochemistry and Biophysics, University of Pennsylvania, Philadelphia, PA 19104, USA.
Ismail A
IA
Ahmed
Department of Chemistry, University of Puerto Rico at Cayey, Cayey 00736, Puerto Rico.
Mariana I León
MI
Berríos
Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104, USA. Electronic address: gai@sas.upenn.edu.
Feng
F
Gai
D000409:Alanine / Q000031:analogs & derivatives* / Q000737:chemistry; D000588:Amines / Q000737:chemistry; D002462:Cell Membrane / Q000378:metabolism*; D057846:Cell-Penetrating Peptides / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009570:Nitriles / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D010649:Phenylalanine / Q000031:analogs & derivatives
D000409:Alanine; D000588:Amines; D057846:Cell-Penetrating Peptides; D009570:Nitriles; C530634:p-cyanophenylalanine; D010649:Phenylalanine
Cell-penetrating peptide; Fluorescence spectroscopy; N-terminal pK(a) of peptide; p-Cyanophenylalanine; pH sensor