TAIL-SPECIFIC ANTIBODIES THAT BLOCK RETURN OF 46,000 M(R) MANNOSE 6-PHOSPHATE RECEPTOR TO THE TRANS-GOLGI NETWORK

Recycling of 46,000 M(r) mannose 6-phosphate receptor (MPR 46) was inv estigated by microinjection of F(ab) fragments against small epitopes within the cytoplasmic domain of the receptor. F(ab) fragments against the peptide 43-47 (Ala-Tyr-Arg-Gly-Val) efficiently blocked return of MPR 46 to the TGN. Antibody-induced redistribution resulted in accumu lation of MPR 46 within an endosomal compartment, from which it recycl ed to the plasma membrane. Rab5 and rab7, markers for early and late e ndosomes, respectively, were not detectable in the compartment of redi stributed MPR 46, suggesting that it represents a specialized endosoma l subcompartment. The bulk of redistributed MPR 46 did not colocalize with endocytosed fluid-phase marker, suggesting that it accumulates at a site where MPR 46 has been segregated from endocytosed material, wh ich is destined for transport to lysosomes. Peptide 43-47 contains a t yrosine (residue 44) which has been shown earlier to be part of an int ernalization signal for MPR 46 (Johnson, K. E, W. Chan, and S. Kornfel d. 1990. Proc. Natl. Acad. Sci. USA. 87:10010-10014). The role of tyro sine residue 44 as part of a putative multifunctional sorting signal i s discussed.