Comparative analysis by two-dimensional iodopeptide mapping of the RhD protein and LW glycoprotein

The RhD polypeptide and LW glycoprotein were separately immunopurified with monoclonal antibodies and compared by two-dimensional (2-D) iodopeptide mapping after digestion with alpha-chymotrypsin. These proteins have distinct 2-D maps, as seen after 125I-labeling tyrosine residues (chloramine-T procedure), and even more strikingly after labeling primary amine residues (Bolton-Hunter procedure). Of the more than 20 iodopeptides visualized, only five migrated identically when preparations of RhD and LW were directly compared, suggesting that RhD and LW are different proteins that may share some common protein domains. N-glycanase treatment of the iodopeptides did not modify the 2-D map of the RhD protein but greatly affected the LW map, further indicating that LW, but not RhD, carries N-linked carbohydrate chains. After deglycosylation the LW map was different from the RhD map, confirming that the RhD and LW polypeptides are different proteins. These findings demonstrate that LW is neither a glycosylated form of Rh protein nor is Rh a precursor of LW.