Application of proteomics to the characterization of beta-lactoglobulin genetic variants by capillary electrophoresis-mass spectrometry and nano-liquid chromatography-mass spectrometry-mass spectrometry.

This report presents an analytical strategy for the identification of beta-lactoglobulin (beta-Lg) variants or isoforms in bovine milk by using capillary electrophoresis-electrospray ionization-mass spectrometry (CE-ESI-MS) and nano-liquid chromatography-electrospray-mass spectrometry-mass spectrometry (nano-LC-ESI-MS-MS). beta-Lg isoforms were separated and collected by CE, and their molecular masses were determined by CE-ESI-MS. Protein isoforms collected by CE were digested with trypsin and analyzed by nano-LC-ESI-MS-MS. Isoforms analyzed by CE-ESI-MS presented multiply charged ions that after deconvolution resulted in molecular masses of 18,364 +/- 1.0 Da and 18,279 +/- 2.0 Da. Fragmentation of parent ions in MS-MS experiments of specific tryptic peptides were carried out to identify beta-Lg variants in milk samples. The milk samples analyzed were indeed phenotypes AA, BB, or AB.