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

摘要

Alpha-lactalbumin (α-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 a-la protein structure during hydrolysis and nanotube formation using optical spectroscopy. Before spectroscopic measurements, nanotubes were examined with microscopy. The observed a-la nanotubes (α-LaNTs) were in the form of regular hollow strands with a diameter of about 20 nm and the average length of 1 urn. Amide and backbone vibration bands of the Raman spectra displayed remarkable conformational changes in a and β domains in the protein structure during nanotube growth. This was confirmed by the Fourier-transform infrared (FTIR) spectroscopy data. Also, FTlR analysis revealed certain bands at calcium (Ca~(++)) binding sites of COO~- groups in hydrolysed protein. These sites might be critical in nanotube elongation.