Glycation pattern of peptides condensed with maltose, lactose and glucose determined by ultraviolet matrix-assisted laser desorption/ionization tandem mass spectrometry.

Protein glycation is the non-enzymatic condensation of sugars with proteins. Although commonly occurring in both the therapeutic and food/beverage industries, protein glycation has not been the focus of many proteomic investigations. This study aims to establish a reliable mass spectrometric method for screening large tandem mass spectrometric (MSMS) datasets for protein glycation with glucose, lactose and maltose. Control experiments using a standard peptide containing a single glycation site led to the discovery of characteristic neutral loss fragmentation patterns in MSMS analysis for glucose, lactose and maltose condensed with peptides. Valid in both tandem time-of-flight (TOFTOF) and quadrupole ion trap time-of-flight matrix-assisted laser desorption/ionization (QIT TOF MALDI) mass spectrometers, these neutral loss signatures were then applied to elucidation of modified peptides from a complex human serum albumin (HSA) digest glycated with each of the proposed sugars. Screening of these large datasets was made possible by specifically designed software solutions that enable the input of detailed user-defined post-translational modifications that are not included in the universally available databases such as Unimod.