Characterization of a novel affinity binding ligand for tyrosine nitrated peptides from a phage-displayed peptide library.

As an important post-translational modification in response to oxidative and nitrosative stress, protein tyrosine nitration is deeply involved in many physiological and pathological processes. Identifying tyrosine nitration in proteins is challenging due to its low abundance.Consequently, pre-separation and enrichment of tyrosine-nitrated peptides (TNPs) are necessary before submitting them to mass spectrometry analysis. However, the most popularly used anti-nitrotyrosine antibody pull-down method showed limitations like sequence preference and unspecific binding. Therefore, developing novel affinity purification materials for TNPs is of significance. In the present study, we screened the phage-displayed 12-mer randomized peptide library for affinity binding peptide of the synthetic standard TNP (sTNP, sequence: HN-GGGGY*GGG-COOH) and identified a peptide named NT-1 (HN-TLWPFDLWLKTR-COOH) as a promising candidate. NT-1 at extremely low concentration (3 nM) in solutions could be efficiently captured by immobilized sTNP as determined by pull-down and subsequent MALDI-TOF MS analysis. Surface plasmon resonance (SPR) measurement confirmed that NT-1 possesseed a good selectivity, showing more than 100-fold higher binding affinity with TNP than its non-nitrated counterpart. Moreover, NT-1 could efficiently capture various types of TNPs in solutions even in the presence of 1000-fold excessive amount of trypsinized BSA fragments. Most importantly, NT-1 showed superiority to commercially used nitrotyrosine antibody as the former captured more TNPs, with less sequence preference. In summary, our study provided NT-1 as a novel affinity binding ligand for TNPs and should be useful in developing an alternative enrichment strategy for TNPs.