Temperature- and pH-induced multiple partially unfolded states of recombinant human interferon-alpha2a: possible implications in protein stability.
OBJECTIVE
To study the effect of solution conditions on the structural conformation of recombinant human interferon-alpha2a (IFNalpha2a) to investigate its tendency to form partially unfolded intermediates.


METHODS
The structural properties of IFNalpha2a were studied at various pH values (2.0-7.4) and temperatures (5 degrees C-80 degrees C) using Trp fluorescence emission, fluorescence quenching, near- and far-UV circular dichroism (CD) spectroscopy, and DSC.


RESULTS
Fluorescence intensity measurements as a function of temperature indicated the onset of the thermal unfolding of IFNalpha2a, denoted by Td, around 60 degrees C above pH 4.0. Td was not observed at pH 3.5 and below. Acrylamide and iodide quenching studies indicated partial unfolding of protein with decrease in pH and with increase in temperature up to 50 degrees C. Near-UV CD studies indicated a significant loss in the tertiary structure of protein on increase in temperature from 15 degrees C to 50 degrees C at all solution pHs. DSC scans supported results obtained from fluorescence and CD studies at pH 4.0 and below. DSC, however, was insensitive to changes that occurred at moderate temperatures at pH 5.0 and 7.4.


CONCLUSIONS
IFNalpha2a has a tendency to acquire multiple partially unfolded states with structural conformations sensitive to solution pH and temperature. These states were formed at moderate temperatures, and it is speculated that these partially unfolded states could play an important role in the aggregation of proteins during the long-term storage of aqueous protein formulations.
Sharma
Vikas K
VK
Department of Pharmaceutical Sciences, University of Connecticut, Storrs, CT 06269, USA.
Kalonia
Devendra S
DS
D002152:Calorimetry, Differential Scanning; D002942:Circular Dichroism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D000077190:Interferon alpha-2; D016898:Interferon-alpha / Q000032:analysis* / Q000737:chemistry; D017510:Protein Folding; D011994:Recombinant Proteins; D013050:Spectrometry, Fluorescence; D013696:Temperature; D013816:Thermodynamics
D000077190:Interferon alpha-2; D016898:Interferon-alpha; D011994:Recombinant Proteins