title: Do guanidinium and tetrapropylammonium ions specifically interact with aromatic amino acid side chains?
abstract: Many ions are known to affect the activity, stability, and structural integrity of proteins. Although this effect can be generally attributed to ion-induced changes in forces that govern protein folding, delineating the underlying mechanism of action still remains challenging because it requires assessment of all relevant interactions, such as ion-protein, ion-water, and ion-ion interactions. Herein, we use two unnatural aromatic amino acids and several spectroscopic techniques to examine whether guanidinium chloride, one of the most commonly used protein denaturants, and tetrapropylammonium chloride can specifically interact with aromatic side chains. Our results show that tetrapropylammonium, but not guanidinium, can preferentially accumulate around aromatic residues and that tetrapropylammonium undergoes a transition at ∼1.3 M to form aggregates. We find that similar to ionic micelles, on one hand, such aggregates can disrupt native hydrophobic interactions, and on the other hand, they can promote α-helix formation in certain peptides.
authors.affiliation: Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104.|Ultrafast Optical Processes Laboratory, University of Pennsylvania, Philadelphia, PA 19104.
authors.forename: Bei
authors.initials: B
authors.lastname: Ding
authors.affiliation: Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104.
authors.forename: Debopreeti
authors.initials: D
authors.lastname: Mukherjee
authors.affiliation: Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104.|Ultrafast Optical Processes Laboratory, University of Pennsylvania, Philadelphia, PA 19104.
authors.forename: Jianxin
authors.initials: J
authors.lastname: Chen
authors.affiliation: Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104; gai@sas.upenn.edu.|Ultrafast Optical Processes Laboratory, University of Pennsylvania, Philadelphia, PA 19104.
authors.forename: Feng
authors.initials: F
authors.lastname: Gai
mesh_terms: D000409:Alanine / Q000031:analogs & derivatives* / Q000737:chemistry / Q000187:drug effects; D024322:Amino Acids, Aromatic / Q000737:chemistry / Q000187:drug effects*; D023181:Antimicrobial Cationic Peptides / Q000737:chemistry; D002942:Circular Dichroism; D019791:Guanidine / Q000737:chemistry / Q000494:pharmacology*; D057927:Hydrophobic and Hydrophilic Interactions; D009570:Nitriles / Q000737:chemistry; D010455:Peptides / Q000737:chemistry; D011489:Protein Denaturation; D055550:Protein Stability / Q000187:drug effects; D017433:Protein Structure, Secondary / Q000187:drug effects; D000644:Quaternary Ammonium Compounds / Q000737:chemistry / Q000494:pharmacology*; D012997:Solvents; D013050:Spectrometry, Fluorescence; D013055:Spectrophotometry, Infrared / Q000379:methods*; D017550:Spectroscopy, Fourier Transform Infrared; D010649:Phenylalanine / Q000031:analogs & derivatives
chemical_list: D000409:Alanine; D024322:Amino Acids, Aromatic; D023181:Antimicrobial Cationic Peptides; D019791:Guanidine; D009570:Nitriles; D010455:Peptides; D000644:Quaternary Ammonium Compounds; D012997:Solvents; C530634:p-cyanophenylalanine; D010649:Phenylalanine; C052377:tetrapropylammonium; C019529:polyalanine
keywords: 2D IR; Hofmeister ions; guanidinium; tetrapropylammonium; unnatural amino acid