Azide-alkyne cycloaddition-mediated cyclization of phosphonopeptides and their evaluation as PTP1B binders and enrichment tools

Peptide probes containing a non-hydrolyzable phosphotyrosine-mimetic residue for enrichment of protein tyrosine phosphatases

We developed peptide probes containing a non-hydrolyzable phosphotyrosine mimetic, 4-[difluoro(phosphono)methyl]-L-phenylalanine (F₂ Pmp) for enrichment of protein tyrosine phosphatases (PTPs). We found that different F₂ Pmp probes can enrich different PTPs, depending on the probe sequence. Furthermore, proteins containing a Src homology 2 (SH2) domain were enriched together. Importantly, probes containing phosphotyrosine instead of F₂ Pmp failed to enrich PTPs due to dephosphorylation during the pulldown step. This enrichment approach using peptides containing F₂ Pmp could be a generic tool for tyrosine phosphatome analysis without the use of antibodies. This article is protected by copyright. All rights reserved.

A Stable Pyrophosphoserine Analog for Incorporation into Peptides and Proteins

Protein pyrophosphorylation is a covalent modification of proteins, mediated by the inositol pyrophosphate messengers. Although the inositol pyrophosphates have been linked to a range of cellular processes, the role of protein pyrophosphorylation remains minimally characterized in vivo. The inherent instability of the phosphoanhydride bond has hampered the development of useful bioanalytical techniques to interrogate this novel signaling mechanism. Here, we describe the preparation of a pyrophosphoserine analog containing a stable methylene-bisphosphonate group that is compatible with solid-phase peptide synthesis. The resulting peptides demonstrate enhanced stability in Eukaryotic cell lysates and mammalian plasma and display resistance toward chemical degradation, when compared to the corresponding pyrophosphopeptides. In addition, the peptides containing the stable pyrophosphoserine analog are highly compatible with common ligation methods, such as native chemical ligation, maleimide conjugation, and glutaraldehyde ligation. The bisphosphonate-containing peptides will, therefore, be well-suited for future pyrophosphoserine antibody generation and affinity capture of pyrophosphoprotein binding partners and provide a key entry point to study the regulatory role of protein pyrophosphorylation.

Prediction and verification of novel peptide targets of protein tyrosine phosphatase 1B

Phosphotyrosine peptides are useful starting points for inhibitor design and for the search for protein tyrosine phosphatase (PTP) phosphoprotein substrates. To identify novel phosphopeptide substrates of PTP1B, we developed a computational prediction protocol based on a virtual library of protein sequences with known phosphotyrosine sites. To these we applied sequence-based methods, biologically meaningful filters and molecular docking. Five peptides were selected for biochemical testing of their potential as PTP1B substrates. All five peptides were equally good substrates for PTP1B compared to a known peptide substrate whereas appropriate control peptides were not recognized, showing that our protocol can be used to identify novel peptide substrates of PTP1B.