An asparaginyl endopeptidase processes a microbial antigen for class II MHC presentation

Bénédicte Manoury, Eric W. Hewitt, Nick Morrice, Pam M. Dando, Alan J. Barret, Colin Watts (Lead / Corresponding author)

    Research output: Contribution to journalArticlepeer-review

    321 Citations (Scopus)

    Abstract

    Foreign protein antigens must be broken down within endosomes or lysosomes to generate suitable peptides that will form complexes with class II major histocompatibility complex molecules for presentation to T cells. However, it is not known which proteases are required for antigen processing. To investigate this, we exposed a domain of the microbial tetanus toxin antigen (TTCF) to disrupted lysosomes that had been purified from a human B- cell line. Here we show that the dominant processing activity is not one of the known lysosomal cathepsins, which are generally believed to be the principal enzymes involved in antigen processing, but is instead an asparagine-specific cysteine endopeptidase. This enzyme seems similar or identical to a mammalian homologue of the legumain/haemoglobinase asparaginyl endopeptidases found originally in plants and parasites. We designed competitive peptide inhibitors of B-cell asparaginyl endopeptidase (AEP) that specifically block its proteolytic activity and inhibit processing of TTCF in vitro. In vivo, these inhibitors slow TTCF presentation to T cells, whereas preprocessing of TTCF with AEP accelerates its presentation, indicating that this enzyme performs a key step in TTCF processing. We also show that N- glycosylation of asparagine residues blocks AEP action in vitro. This indicates that N-glycosylation could eliminate sites of processing by AEP in mammalian proteins, allowing preferential processing of microbial antigens.

    Original languageEnglish
    Pages (from-to)695-699
    Number of pages5
    JournalNature
    Volume396
    Issue number6712
    DOIs
    Publication statusPublished - 17 Dec 1998

    ASJC Scopus subject areas

    • General

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