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.
Highlights
Proteins play a critical role in biological processes and often require an aqueous phase to be transported to their target sites
Several papers have focused on the prediction of the dynamic transition in hydrated macromolecules using different techniques, including neutron scattering, Mossbauer spectroscopy, and X-ray diffraction [3,4,5]
In this paper we present a fundamental study of hydrated GP2 using THz time domain spectroscopy
Summary
Proteins play a critical role in biological processes and often require an aqueous phase to be transported to their target sites. A variety of experiments have demonstrated that proteins influence both the spatial and dynamic arrangement of neighboring liquid layers through weak intermolecular interactions [1] This dynamical process can be considered as being described by collective vibrational modes, individual bond vibrations and determined by the energy necessary for motion relative to the ambient temperature [2]. It is widely believed that this temperature is affected by many factors, e.g. molecular weight [6,7], bond interactions [8], polar groups [9] and backbone flexibility [10], different results have been reported for the same protein type depending on the detection method [8,10] This dynamical phenomenon has not been intensely studied at terahertz (THz) frequencies and motivates further fundamental research
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