| Abstract: | Formyl peptide chemotactic receptors affinity-labeled with N-formyl-Nle-Leu-Phe-Nle-[125I]iodo-Tyr-Lys (where Nle represents norleucine) and ethylene glycol bis(succinimidyl succinate) consist of two isoelectric forms with cell type differences in both apparent size and charge (neutrophils: 55-70 kDa, pI 5.8, and 6.2.; monocytes: 60-75 kDa, pI 5.6 and 6.0; differentiated HL-60 cells: 62-85 kDa, pI 5.6 and 6.0). Endo-beta-N-acetylglucosaminidase F (endo F) cleavage of N-linked oligosaccharides from formyl peptide receptor generates 40-50- and 33-kDa products that can be affinity-labeled. Whereas both pI forms of this receptor from neutrophils are cleaved by endo F to 33-kDa final products, this cleavage does not eliminate pI differences. Tunicamycin decreases expression of formyl peptide receptor on differentiating HL-60 and causes a dose-dependent decrease in size of the major product seen after affinity labeling (0.5 micrograms/ml: 38-48 kDa; 2 micrograms/ml: 32 kDa). Thus, the formyl peptide receptor polypeptide backbone from all three cell types contains at least two N-linked oligosaccharide side chains which contribute to the cell type differences in Mr and are not required for ligand binding. Papain treatment of intact cells generates a membrane-bound formyl peptide receptor fragment that can be affinity-labeled and is of similar size (29-31 kDa) in all three cell types. Endo F treatment of the affinity-labeled papain fragment of formyl peptide receptor does not alter its size, suggesting that this fragment does not contain the N-linked oligosaccharide cleaved by endo F from intact receptor. The results indicate that at least two N-linked oligosaccharide chains are located on the distal 1-3-kDa portion of the receptor polypeptide backbone. |
