The human CD10 lacking an N-glycan at Asn₆₂₈ is deficient in surface expression and neutral endopeptidase activity

Background: CD10, also known as neprilysin or enkephalinase exhibiting neutral endopeptidase (NEP) activity, is expressed by B-lineage hematopoietic cells as well as a variety of cells from normal tissues. It cleaves peptides such as cytokines to act for terminating inflammatory responses. Although CD10 molecules of the human pre-B-cell line NALM-6 have 6 consensus N-glycosylation sites, three of them are known to be N-glycosylated by X-ray crystallography. Methods: In order to investigate the role of N-glycans in the full expression of NEP activity, we modified N-glycans by treatment of NALM6 cells with various glycosidases or alter each of the consensus N-glycosylation sites by generating site-directed mutagenesis and compared the NEP activities of the sugar-altered CD10 with those of intact CD10. Results: CD10 of the human B-cell line NALM-6 was dominantly localized in raft microdomains and heterogeneously N-glycosylated. Although neither desialylation nor further degalactosylation caused defective NEP activity, removal of only a small part of N-glycans by treatment with glycopeptidase F under non-denaturing conditions decreased NEP activity completely. All of the three consensus sites of CD10 in HEK293 cells introduced with wild type-CD10 were confirmed to be N-glycosylated. Surface expression of N-glycan at Asn₆₂₈-deleted CD10 by HEK293 cells was greatly decreased as well as it lost entire NEP activities. Conclusions: N-glycosylation at Asn₆₂₈ is essential not only for NEP activities, but also for surface expression. General significance: Quality control system does not allow dysfunctional ecto-type proteases to express on plasma membrane.