Investigation of the structure of alpha- lactalbumin protein nanotubes using optical spectroscopy

Alpha-lactalbumin (-la) is one of the major proteins in whey. When partially hydrolysed with Bacillus licheniformis protease, it produces nanotubular structures in the presence of calcium ions by a self-assembly process. This study presents investigation of -la protein structure during hydrolysis and nanotube formation using optical spectroscopy. Before spectroscopic measurements, nanotubes were examined with microscopy. The observed -la nanotubes (-LaNTs) were in the form of regular hollow strands with a diameter of about 20nm and the average length of 1m. Amide and backbone vibration bands of the Raman spectra displayed remarkable conformational changes in and domains in the protein structure during nanotube growth. This was confirmed by the Fourier-transform infrared (FTIR) spectroscopy data. Also, FTIR analysis revealed certain bands at calcium (Ca++) binding sites of COO- groups in hydrolysed protein. These sites might be critical in nanotube elongation.