Dimeric analogs of immunosuppressive decapeptide fragment of ubiquitin

Abstract

Our previous studies revealed that ubiquitin and its decapeptide fragment with the LEDGRTLSDY sequence, located on the exposed molecule loop, strongly suppressed the immune response. This suggested that the loop may serve as a functional epitope of ubiquitin molecule and that a possible mechanism of biological action of the synthesized peptides is associated with interfering in interactions of ubiquitin with other molecules. Ubiquitin is known to exist in oligomeric forms, which can interact with various oligomeric receptors. We designed and synthesized new dimeric analogs of the ubiquitin fragment, to probe whether dimeric peptides may have higher affinity towards the ubiquitin receptors responsible for immunosuppression, which are believed to form oligomeric structures. Three dimerization strategies, N-terminus to N-terminus, C-terminus to C-terminus, and N-terminus to C-terminus (head-to-tail) via PEG derivatives were used to synthesize the dimeric peptides on solid support. In the course of our research, we developed a new and straightforward procedure of dimerization where α-amino groups of the C-terminal lysine residues of two peptide fragments were linked by PEG spacer directly on solid support. The effect of dimeric analogs on the immunological response was tested in the AFC in vitro experiment. The immunological tests showed that the head-to-tail dimerization caused a more profound increase in the biological activity than other tested dimerization methods. Our results suggest that such orientation of peptide components may correspond to orientation of the hypothetic ubiquitin receptors responsible for the immunomodulatory activity.

Analysis of Fragmentation Pathways of Peptide Modified with Quaternary Ammonium and Phosphonium Group as Ionization Enhancers

“…In our study, we examined the effect of both the quaternary ammonium (QAS)/ phosphonium (QPS) group and the side chain of amino acid residues on the fragmentation pathway of a series of the model peptide with the H-GDGRTL-NH 2 peptide analogues as an immunosuppressive ubiquitin fragment [29]. The major novelty of the presented manuscript is the presentation and comparison of the CID and ECD spectra for the peptide modified by different fixed-charge tags, which has not been presented before in the scientific literature.…”

Evidence of an Antimicrobial Peptide Signature Encrypted in HECT E3 Ubiquitin Ligases

“…Ubiquitin degradation produces host defense peptides (HDPs) (22–28), pivotal players in the innate defense against microbial pathogens (17–19). Additionally, more than 70 immunosuppressive peptides have been discovered originating from ubiquitin degradation in vitro (22, 30, 31). However, production of antimicrobial and immunomodulatory peptides is a complex, multilayered process (17–19, 22, 26, 28, 30, 31): it involves the canonical expression of transcriptionally regulated gene-encoded peptides (17–19) and fast production of cryptic peptides [that is, release of protein fragments with distinct properties from that of the original protein (19, 22, 26, 28)].…”

“…Additionally, more than 70 immunosuppressive peptides have been discovered originating from ubiquitin degradation in vitro (22, 30, 31). However, production of antimicrobial and immunomodulatory peptides is a complex, multilayered process (17–19, 22, 26, 28, 30, 31): it involves the canonical expression of transcriptionally regulated gene-encoded peptides (17–19) and fast production of cryptic peptides [that is, release of protein fragments with distinct properties from that of the original protein (19, 22, 26, 28)]. Therefore, the UPP orchestrates biologically active peptide production in both the innate and the adaptive metazoan immune systems by generating the recently discovered ubiquitin-encrypted HDPs (22–28), E3-mediated transcriptional regulation of host defense gene expression (3, 4, 6, 7, 10), and production of short fragments for MHC class I-mediated antigen presentation (3, 4, 8, 9, 16).…”