Publication Date:
2012-04-05
Description:
Scavenger receptor expressed by endothelial cells (SREC-I) mediates the endocytosis of chemically modified lipoproteins such as acetylated low-density lipoprotein (Ac-LDL) and oxidized LDL and is implicated in atherogenesis. We produced recombinant SREC-I in Chinese hamster ovary-K1 cells and identified three potential glycosylation sites, Asn 289 , Asn 382 and Asn 393 , which were all glycosylated. To determine the function of N -glycans in SREC-I, we characterized SREC-I mutant proteins by intracellular distribution and the cellular incorporation rate of Ac-LDL. N382Q/N393Q and N289Q/N382Q/N393Q were sequestered in the endoplasmic reticulum, resulting in a severe reduction in the cellular incorporation of Ac-LDL. N382Q showed a normal cell surface residency and an enhanced affinity for Ac-LDL, resulting in an elevated Ac-LDL cellular incorporation. These results indicate that the N -glycan of Asn 393 regulates the intracellular sorting of SREC-I and that the N -glycan of Asn 382 controls ligand-binding affinity. Furthermore, we detected an enhanced trypsin sensitivity of the N289Q. Glycan structure analyses revealed that the core-fucosylated bi-antennary is the common major structure at all glycosylation sites. In addition, tri- and tetra-antennary were detected as minor constituents at Asn 289 . A bisecting GlcNAc was also detected at Asn 382 and Asn 393 . Structural analyses and homology modeling of SREC-I suggest that the N -glycan bearing a β1-6GlcNAc branch at Asn 289 protects from proteinase attack and thus confers a higher stability on SREC-I. These data indicate that Asn 289 -, Asn 382 - and Asn 393 -linked N -glycans of SREC-I have distinct functions in regulating proteolytic resistance, ligand-binding affinity and subcellular localization, all of which might be involved in the development of atherogenesis.
Print ISSN:
0959-6658
Electronic ISSN:
1460-2423
Topics:
Biology
,
Medicine
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