Native state conformational heterogeneity of HP35 revealed by time-resolved FRET.
The villin headpiece subdomain (HP35) has become one of the most widely used model systems in protein folding studies, due to its small size and ultrafast folding kinetics. Here, we use HP35 as a test bed to show that the fluorescence decay kinetics of an unnatural amino acid, p-cyanophenylalanine (Phe(CN)), which are modulated by a nearby quencher (e.g., tryptophan or 7-azatryptophan) through the mechanism of fluorescence resonance energy transfer (FRET), can be used to detect protein conformational heterogeneity. This method is based on the notion that protein conformations having different donor-acceptor distances and interconverting slowly compared to the fluorescence lifetime of the donor (Phe(CN)) would exhibit different donor fluorescence lifetimes. Our results provide strong evidence suggesting that the native free energy basin of HP35 is populated with conformations that differ mostly in the position and mean helicity of the C-terminal helix. This finding is consistent with several previous experimental and computational studies. Moreover, this result holds strong implications for computational investigation of the folding mechanism of HP35.
Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States.
Arnaldo L
AL
Serrano
Osman
O
Bilsel
Feng
F
Gai
D000409:Alanine / Q000031:analogs & derivatives / Q000737:chemistry; D031541:Fluorescence Resonance Energy Transfer; D007700:Kinetics; D008840:Microfilament Proteins / Q000737:chemistry* / Q000378:metabolism; D009570:Nitriles / Q000737:chemistry; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D014364:Tryptophan / Q000031:analogs & derivatives / Q000737:chemistry; D010649:Phenylalanine / Q000031:analogs & derivatives
D000409:Alanine; D008840:Microfilament Proteins; D009570:Nitriles; D014364:Tryptophan; C530634:p-cyanophenylalanine; D010649:Phenylalanine; C026615:villin; C006657:7-azatryptophan