N-glycomic and N-glycoproteomic studies in the social amoebae.

N-glycans modify the great majority of all secreted and plasma membrane proteins, which themselves constitute one-third to one-half of the proteome. The ultimate definition of the glycoproteome would be the identification of all the N-glycans attached to all the modified asparaginyl sites of all the proteins, but glycosylation heterogeneity makes this an unachievable goal. However, mass spectrometry in combination with other methods does have the power to deeply mine the N-glycome of Dictyostelium, and characterize glycan profiles at individual sites of glycoproteins. Recent studies from our laboratories using mass spectrometry-based methods have confirmed basic precepts of the N-glycome based on prior classical methods using radiotracer methods, and have extended the scope of glycan diversity and the distribution of glycan types across specific glycoprotein attachment sites. The protocols described here simplify studies of the N-glycome and -glycoproteome, which should prove useful for interpreting mutant phenotypes, conducting interstrain and interspecies comparisons, and investigating glycan functions in glycoproteins of interest.