Far-infrared spectroscopy of protein higher-order structures.

Far-infrared (FIR) spectroscopy in the spectral region of 50-450 cm(-1) was used to study a series of protein higher-order structures constructed using β-lactoglobulin and polyomavirus capsid protein VP1. There were marked differences in the spectra for β-lactoglobulin monomer and dimer and between untreated β-lactoglobulin and heat-induced gels formed at neutral pH. Untreated β-lactoglobulin and heat-induced gels formed at acidic pH exhibited little difference in their spectra. Assembly of the quaternary structure of polyomavirus virus-like particles also caused large changes in the FIR spectra. These findings suggest that FIR spectroscopy may prove useful in studying some protein quaternary and higher-order structures. There was evidence of detection of β-lactoglobulin dimerization, intermolecular disulfide bonding in heat-induced neutral gels, and polyomavirus virus-like particle assembly but no evidence that FIR could detect β-lactoglobulin fibrils with their polymeric structure and hydrogen-bonded intermolecular β-pleated sheeting.