Institute for Chemical Immunology

Leiden, Netherlands

Institute for Chemical Immunology

Leiden, Netherlands
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Berkers C.R.,Netherlands Cancer Institute | Berkers C.R.,Institute for Chemical Immunology | Berkers C.R.,University Utrecht | De Jong A.,Netherlands Cancer Institute | And 12 more authors.
Journal of Immunology | Year: 2015

Peptide splicing, in which two distant parts of a protein are excised and then ligated to form a novel peptide, can generate unique MHC class I-restricted responses. Because these peptides are not genetically encoded and the rules behind proteasomal splicing are unknown, it is difficult to predict these spliced Ags. In the current study, small libraries of short peptides were used to identify amino acid sequences that affect the efficiency of this transpeptidation process. We observed that splicing does not occur at random, neither in terms of the amino acid sequences nor through random splicing of peptides from different sources. In contrast, splicing followed distinct rules that we deduced and validated both in vitro and in cells. Peptide ligation was quantified using a model peptide and demonstrated to occur with up to 30% ligation efficiency in vitro, provided that optimal structural requirements for ligation were met by both ligating partners. In addition, many splicing products could be formed from a single protein. Our splicing rules will facilitate prediction and detection of new spliced Ags to expand the peptidome presented by MHC class I Ags. Copyright © 2015 by The American Association of Immunologists, Inc.


Berkers C.R.,Netherlands Cancer Institute | Berkers C.R.,Institute for Chemical Immunology | Berkers C.R.,University Utrecht | De Jong A.,Netherlands Cancer Institute | And 8 more authors.
Journal of Immunology | Year: 2015

The proteasome is able to create spliced Ags, in which two distant parts of a protein are excised and ligated together to form a novel peptide, for presentation by MHC class I molecules. These noncontiguous epitopes are generated via a transpeptidation reaction catalyzed by the proteasomal active sites. Transpeptidation reactions in the proteasome follow explicit rules and occur particularly efficiently when the C-terminal ligation partner contains a lysine or arginine residue at the site of ligation. Lysine contains two amino groups that theoretically may both participate in ligation reactions, implying that potentially not only peptide but also isopeptide linkages could be formed. Using nuclear magnetic resonance spectroscopy, we demonstrate in the present study that the proteasome can use the ε-amino group of an N-terminal lysine residue in transpeptidation reactions to create a novel type of posttranslationally modified epitopes. We show that the overall efficiency of ε ligation is only 10-fold lower as compared with α ligation, suggesting that the proteasome can produce sufficient isopeptide Ag to evoke a T cell response. Additionally, we show that isopeptides are more stable toward further proteasomal processing than are normal peptides, and we demonstrate that isopeptides can bind to HLA-A2.1 and HLA-A3 with high affinity. These properties likely increase the fraction of ε-ligated peptides presented on the cell surface for CD8+ T cell surveillance. Finally, we show that isopeptide Ags are immunogenic in vivo. We postulate that ε ligation is a genuine posttranslational modification, suggesting that the proteasome can create a novel type of Ag that is likely to play a role in immunity. Copyright © 2015 by The American Association of Immunologists, Inc.


van Elsland D.M.,Leiden University | van Elsland D.M.,Institute for Chemical Immunology | Bos E.,Leiden University | Overkleeft H.S.,Leiden University | And 4 more authors.
Journal of Chemical Biology | Year: 2015

With correlative light and electron microscopy (CLEM), the ultrastructural cellular location of a biomolecule of interest can be determined using a combination of light microscopy (LM) and electron microscopy (EM). In many cases, the application of CLEM requires the use of markers that need to be attached to a biomolecule of interest to allow its identification and localization. Here, we review the potential of bioorthogonal chemistry to introduce such markers for CLEM. © 2015, The Author(s).


Pang B.,Netherlands Cancer Institute | De Jong J.,Netherlands Cancer Institute | Qiao X.,Netherlands Cancer Institute | Wessels L.F.A.,Netherlands Cancer Institute | And 2 more authors.
Nature Chemical Biology | Year: 2015

Many anticancer drugs induce DNA breaks to eliminate tumor cells. The anthracycline topoisomerase II inhibitors additionally cause histone eviction. Here, we performed genome-wide high-resolution mapping of chemotherapeutic effects of various topoisomerase I and II (TopoI and II) inhibitors and integrated this mapping with established maps of genomic or epigenomic features to show their activities in different genomic regions. The TopoI inhibitor topotecan and the TopoII inhibitor etoposide are similar in inducing DNA damage at transcriptionally active genomic regions. The anthracycline daunorubicin induces DNA breaks and evicts histones from active chromatin, thus quenching local DNA damage responses. Another anthracycline, aclarubicin, has a different genomic specificity and evicts histones from H3K27me3-marked heterochromatin, with consequences for diffuse large B-cell lymphoma cells with elevated levels of H3K27me3. Modifying anthracycline structures may yield compounds with selectivity for different genomic regions and activity for different tumor types. © 2015 Nature America, Inc. All rights reserved.

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