Identifying N-linked glycan moiety and motifs in the cysteine-rich domain critical for N-glycosylation and intracellular trafficking of SR-AI and MARCO.

ABSTRACT

BACKGROUND: The accumulation of soluble oligomeric amyloid-ß peptide (oAß) proceeding the formation of senile plaques contributes to synaptic and memory deficits in Alzheimer's disease. Our previous studies have indentified scavenger receptor A (SR-A), especially SR-A type I (SR-AI), as prominent scavenger receptors on mediating oAß clearance by microglia while glycan moiety and scavenger receptor cysteine-rich (SRCR) domain may play the critical role. Macrophage receptor with collagenous structure (MARCO), another member of class A superfamily with a highly conserved SRCR domain, may also play the similar role on oAß internalization. However, the role of N-glycosylation and SRCR domain of SR-AI and MARCO on oAß internalization remains unclear. RESULT: We found that oAß internalization was diminished in the cells expressing SR-AI harboring mutations of dual N-glycosylation sites (i.e. N120Q-N143Q and N143Q-N184Q) while they were normally surface targeted. Normal oAß internalization was observed in 10 SR-AI-SRCR and 4 MARCO-SRCR surface targeted mutants. Alternatively, the SRCR mutants at ß-sheet and α-helix and on disulfide bone formation obstructed receptor's N-glycosylation and surface targeting. CONCLUSION: Our study reveals that N-glycan moiety is more critical than SRCR domain for SR-A-mediated oAß internalization.