Lysosomal Membrane Glycoproteins: Properties of LAMP-1 (Lysosome Associated Membrane Protein) and LAMP-2

摘要

Several properties of the lysosomal membrane glycoproteins LAMP-1 and LAMP-2 have been analyzed. Each molecule was strongly associated with lysosome membranes and was extracted only in the presence of detergent. Studies of the biosynthesis and processing of the glycoproteins showed that each contained a polypeptide core of approximately 43,000 daltons as identified by use of tunicamycin and endoglycosidase H. Concomitant with the increase in apparent molecular weight the molecules became endoglycosidase H resistant and acquired sialic acid residues, indicating that they were converted to complex-type oligosaccharides. The final maturation of the glycoproteins was blocked by monensin. Immunohistochemical analysis of tissues from Balb/c and Beige/J mice showed that the molecules were present on many types of cells, consistent with their presence in lysosomes. The patterns of tissue expression of LAMP-1 and LAMP-2 in the two mouse strains were the same except that the intensity of staining of LAMP-2 was less than that of LAMP-1. LAMP-2, but not LAMP-1, gave a decreased immunofluorescent staining intensity in transformed HaNIH as compared to NIH/3T3 cells. The marked similarities between the LAMP proteins raise the consideration of common functions, possibly associated with the high oligosaccharide content of the molecules. (aw/kt)