Diophantine analysis complements electrospray-Q-TOF data for structure elucidation of transferrin glycoforms used for clinical diagnosis in human serum and cerebrospinal fluid

The use of ESI-Q-TOF in combination with theoretical mapping of possible glycan variants by Diophantine mass analysis allows identification of transferrin (To glycoforms in different biological fluids including human serum and cerebrospinal fluid (CSF). In order to restrict the structural variations, a chromatographic separation (HPLC) of the forms with different number of sialic acids is initially conducted. The individual fractions are purified, preconcentrated, and analyzed by ESI-Q-TOF. The results obtained experimentally are compared with those predicted by Diophantine calculations and the structures proposed. Each one of the found masses can be ascribed to a single Tf glycoform with a mass difference that ranged between -1 and -26 Da (average masses). Thus, the methodology can be used for structural characterization of Tf glycoforms relevant for clinical diagnosis without enzymatic digestion.