Intact protein core structure is essential for protein-binding, mononuclear cell proliferating, and neutrophil phagocytosis-enhancing activities of normal human urinary Tamm–Horsfall glycoprotein

Tamm–Horsfall glycoprotein (THP) is synthesized in the particular sites of renal tubules acting as a defense molecule in the urinary system. In the present study, we found that THP contained high amount of Siaα(2,3)Gal/GalNAc, moderate amount of β(1,4)GlcNAc oligomers and GlcNAc/branched mannose, and low amount of mannose residues, but no Siaα(2,6)Gal/GalNAc, in the side-chains of the molecule. THP exhibited high binding affinity with human TNF-α, IgG, C1q and BSA, moderate binding affinity with IL-8, and low binding affinity with IL-6 and IFN-γ. For exploring the role of carbohydrate side-chains and protein core in the protein-binding and cell-stimulating activities, THP was enzyme-digested with carbohydrate-specific [neuraminidase (Nase), β-galactosidase (Gase)], protein-specific [V8 protease (V8), proteinase K (PaseK)] and glycoconjugate-specific [carboxypeptidase Y (Case), O-sialoglycoprotein endopeptidase (Oase)] degrading enzymes. We found that THP digested with V8, Oase, and PaseK, significantly reduced its protein-binding, mononuclear cell proliferating, and neutrophil phagocytosis-enhancing activities. These results suggest that the intact protein core structure, but not carbohydrate side-chains, is essential for pleotropic functions of THP molecule.