title: Observing the temperature dependent transition of the GP2 peptide using terahertz spectroscopy.
abstract: The GP2 peptide is derived from the Human Epidermal growth factor Receptor 2 (HER2/nue), a marker protein for breast cancer present in saliva. In this paper we study the temperature dependent behavior of hydrated GP2 at terahertz frequencies and find that the peptide undergoes a dynamic transition between 200 and 220 K. By fitting suitable molecular models to the frequency response we determine the molecular processes involved above and below the transition temperature (T(D)). In particular, we show that below T(D) the dynamic transition is dominated by a simple harmonic vibration with a slow and temperature dependent relaxation time constant and that above T(D), the dynamic behavior is governed by two oscillators, one of which has a fast and temperature independent relaxation time constant and the other of which is a heavily damped oscillator with a slow and temperature dependent time constant. Furthermore a red shifting of the characteristic frequency of the damped oscillator was observed, confirming the presence of a non-harmonic vibration potential. Our measurements and modeling of GP2 highlight the unique capabilities of THz spectroscopy for protein characterization.
authors.affiliation: National-Regional Key Technology Engineering Laboratory for Medical Ultrasound, Guangdong Key Laboratory for Biomedical Measurements and Ultrasound Imaging, Department of Biomedical Engineering, School of Medicine, Shenzhen University, Shenzhen, China.
authors.forename: Yiwen
authors.initials: Y
authors.lastname: Sun
authors.forename: Zexuan
authors.initials: Z
authors.lastname: Zhu
authors.forename: Siping
authors.initials: S
authors.lastname: Chen
authors.forename: Jega
authors.initials: J
authors.lastname: Balakrishnan
authors.forename: Derek
authors.initials: D
authors.lastname: Abbott
authors.forename: Anil T
authors.initials: AT
authors.lastname: Ahuja
authors.forename: Emma
authors.initials: E
authors.lastname: Pickwell-Macpherson
mesh_terms: D000042:Absorption; D014408:Biomarkers, Tumor / Q000737:chemistry; D001943:Breast Neoplasms / Q000378:metabolism; D005260:Female; D005583:Fourier Analysis; D006801:Humans; D015233:Models, Statistical; D008970:Molecular Weight; D009991:Oscillometry / Q000379:methods; D010455:Peptides / Q000737:chemistry*; D010825:Physics / Q000379:methods; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000737:chemistry* / Q000378:metabolism; D012031:Refractometry; D012463:Saliva / Q000378:metabolism; D013053:Spectrophotometry / Q000379:methods; D013696:Temperature; D055068:Terahertz Spectroscopy / Q000379:methods*; D013997:Time Factors
chemical_list: D014408:Biomarkers, Tumor; D010455:Peptides; D018719:Erb-b2 Receptor Tyrosine Kinases; C508053:ERBB2 protein, human