Title : Assignment of
O-glycan attachment sites to the hinge-like
regions of human lysosomal membrane
glycoproteins lamp-1 and
lamp-2
Abstract :
- The lysosomal membrane glycoproteins lamp-1 and lamp-2 are extensively glycosylated with a variety of different carbohydrate structures of both N-linked and O-linked type.
- In the present paper, we report the localization of O-linked oligosaccharides exclusively to the hinge-like regions of lamp-1 and lamp-2 isolated from human chronic myelogenous leukemia cells
- In both glycoproteins , the O-glycans appear in clusters
- In lamp-1 , Thr-171, Thr-172, Ser-179, Ser-181, and Ser-183 were fully glycosylated, whereas Ser-169 was partially glycosylated
- In lamp-2 , complete glycosylation was found at Ser-167, Thr-168, Thr-172, Thr-175, Thr-176, Thr-182, and Thr-183 , and partial glycosylation at Ser-179 and Thr-181 , and possibly also at Thr-185
- The amino acid sequences of these O-glycosylation sites are consistent with the previous reports that residues at positions -1 and +3 may influence the glycosylation reaction
- Circular dichroism and nuclear magnetic resonance spectroscopy was used for the structural characterization of a synthetic peptide corresponding to residues 167 to 190 of lamp-1
- The results indicated that the proline-rich O-glycan acceptor region proline-rich O-glycan acceptor region does not adopt any typical periodic structure but differs from random-coil structure
- The circular dichroism spectrum of the peptide is, however, similar to that of porcine submaxillary apomucin
- A significant conformational variability was observed in this region , presumably due to a slow (on the nuclear magnetic resonance time scale) cis-trans isomerization of several proline residues
- These results, taken together, strongly suggest that a hinge region does not display any typical ordered structure
- The presence of O-glycans thus likely protects this region from intralumenal lysosomal proteases