N-Glycosylation profiling of turtle egg yolk: expression of galabiose structure

To understand the roles of species-specific carbohydrates, systematic studies of interspecific glycan analyses are imperative. An extensive series of glycomics studies on approximately 180 kinds of bird eggs have demonstrated that 60-70% of the birds, which are closely related in phylogeny, express the α-Galp-(1→4)-Galp structure on their egg glycoproteins. This prompted us to investigate the glycosylation profiles of eggs from an evolutionarily related organism, a sea turtle (reptilian). We performed N-glycosylation profiling of turtle egg yolk by using HPLC mapping in conjunction with mass spectrometric methods and thereby demonstrated that the α-Galp-(1→4)-Galp groups are displayed on approximately 38% of total N-glycans. Our findings suggest that the ability to express the galabiose structure was acquired at an early stage of diversification in amniotes.