α-Active Pyrylium Salt 2,4,5-Triphenylpyrylium for Improved Mass Spectrometry-Based Detection of Peptides.

Pyrylium salts are considered efficient chemical tags for amino groups. However, the apparent steric selectivity of pyrylium salts limits their application in the field of chemical labeling, especially during the labeling of sterically hindered compounds like amino acids, peptides, and proteins. Herein, we have investigated the effects of the α-substitution of pyrylium salts on their reactivity. We have also investigated the mechanism of nucleophilic reactions with pyrylium salts and further proposed that the reactivity of pyrylium salts mainly depends on the position and type of their substituents. A series of pyrylium salts were synthesized, and a highly active α-monosubstituted pyrylium salt, 2,4,5-triphenylpyrylium, was developed for efficient chemical labeling. All of the 15 amino acids studied were efficiently labeled under optimized reaction conditions. The 2,4,5-triphenylpyrylium salt was highly efficient in comparison to the previously reported 2,4,6-triphenylpyrylium salt developed for lysine-specific modifications. Furthermore, we successfully used 2,4,5-triphenylpyrylium salt for the hydrophobic labeling of peptides and protein hydrolysates. The most striking observation was that the ionization efficiency of short-chain multilabeled peptides in mixed samples, after derivatization, increased by up to 60 times. The increase in ionization efficiency gradually decreased with increasing peptide chain length. During the "soft" collision-induced dissociation (CID) process, the peptide was tagged at the N-terminus with 2,4,5-triphenylpyrylium, producing abundant a-type ions and b-type ions (Δ = 28), which eases the peptide resequencing process and assists in cracking the peptide codes. Moreover, 2,4,5-triphenylpyrylium has been utilized for the proteomic analysis of HeLa cell digests. In addition, 215 additional proteins were identified in the labeled products and the coverage of most proteins was improved.

In situ derivatization of Au nanoclusters via aurophilic interactions of a triphenylphosphine gold(i) salt with neurotransmitters and their rapid MALDI-TOF-MS detection in mice brain tissue extracts.

Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS) has attracted much attention for the detection of small molecules such as neurotransmitters due to its softness, high sensitivity, extensive compatibility and diverse mass analyzers. However, it has been really a difficult challenge to develop a highly specific organic compound as a matrix for the rapid, sensitive and selective detection of neurotransmitters. Herein, we report tris(triphenylphosphine)gold oxonium tetrafluoroborate ([Ph3PAu]3O+BF4-) for the first time as an efficient matrix for the rapid and simultaneous MALDI-MS detection of neurotransmitters. [Ph3PAu]3O+BF4- facilitates the in situ derivatization of gold nanoclusters (Au NCLs) during the interaction with neurotransmitters, which increases their ionization energy by absorbing more ultra-violet (UV) radiation during MALDI-TOF-MS detection. The results show that this [Ph3PAu]3O+BF4- matrix can exhibit a 10-fold faster response time compared to previously reported pyrylium matrices. In addition, [Ph3PAu]3O+BF4- can also provide the simultaneous derivatization of various neurotransmitters, including dopamine (DA), noradrenaline (NAd), serotonin (5-HT), γ-aminobutyric acid (GABA), histamine (H) and tyramine (TY), in mice brain tissue extracts, which can be detected in the MALDI-TOF-MS spectra.

Alpha-Synuclein Dopaminylation Presented in Plasma of Both Healthy Subjects and Parkinson's Disease Patients.

PURPOSE: Alpha-synuclein (α-syn) dopaminylation can lead to the death of dopaminergic neurons in the brain and is a risk factor of Parkinson's disease (PD). This study aims to examine whether such a posttranslational modification (PTM) is presented in human blood plasma. EXPERIMENTAL DESIGN: In vitro reaction simulation between α-syn and dopamine (DA) is conducted to study the biochemical mechanism. Then α-syn from human blood plasma samples is detected by using immunoprecipitation-mass spectrometry (IP-MS). Lastly the levels of endogenous α-syn and α-syn dopaminylation in 88 blood plasma samples from patients with PD, major depressive disorder (MDD), and healthy control (HC) are compared. RESULTS: DA modifies α-syn with the addition of dopamine-quinone (DAQ) into lysine sites of α-syn in vitro and the addition of DAQ and 3,4-dihydroxyphenylacetaldehyde (DOPAL) in plasma samples. The unmodified α-syn between the PD and HC groups showed similar levels. The levels of two peptides, one with lysine 34 (34 K) DAQ modification and the other with lysine 23 (23 K) ubiquitination, are significantly higher in PD and MDD compared with HC. CONCLUSIONS AND CLINICAL RELEVANCE: Thus, α-syn dopaminylation is measurable and might be used to indicatethe presence and progression of neurological disorders.

Fast, sensitive and selective colorimetric gold bioassay for dopamine detection.

Colorimetric detection of dopamine has the advantage of simplicity in operation and instrumentation. Herein, a highly sensitive and selective colorimetric biosensor with fast response has been developed by using 4'-aminobenzo-18-crown-6 (ABCE) and 4-mercaptophenyl boronic acid (MPBA) modified Au nanoparticles. The modified probe shows an excellent detection limit of 6.0 nM of dopamine at a S/N of 2.01 and about 46 nM at a S/N of 3 within microseconds response. It exhibits excellent detection selectivity even in 1000-fold excess of many different interferents like metal ions, uric acid and ascorbic acid. All these may make it fulfill the requirements for in vivo analysis.