Diversity in Gold Finger Structure Elucidated by Traveling‐Wave Ion Mobility Mass Spectrometry

Abstract

Traveling wave ion mobility (TWIM) mass spectrometry (MS) is a powerful method for the structural and conformational analysis of proteins and peptides, enabling the differentiation of isomeric peptides (or proteins) that have the same sequence but are modified at different residues. In this study, the TWIM‐MS technique was used to separate isomeric AuI metallopeptide ions that were formed by ZnII displacement from the parent zinc fingers (ZFs). The synthetic gold finger peptides were derived from the C‐terminus of the HIV nucleocapsid p7 protein (NCp7‐F2) and finger 3 of the Sp1 transcription factor (Sp1‐F3). TWIM‐MS enabled the acquisition of distinct product ion spectra for each isomer, clearly indicating the binding sites for the major conformers in the presence of multiple coordination possibilities. Collision cross‐section measurements showed that the aurated peptide has a slightly more compact structure than the parent zinc compound NCp7‐F2, which showed only one conformation.

Probing the HIV-1 NCp7 Nucleocapsid Protein with Site-Specific Gold(I)–Phosphine Complexes

“…Preparation was as previously published. 17,20,21 An adequate amount of apo-NCP7 F2 or apo-NC was dissolved in water, and 1.2 equiv of zinc acetate was added per zinc core. The pH was adjusted to 7.2−7.4 using a solution of NH 4 OH.…”

“…[AuCl(Et 3 P)] (1) was synthesized by an adaptation of an already published method. 14,17 In brief, H[AuCl 4 ] (0.50 mmol, 194 mg) was dissolved in 1.0 mL of distilled water, and the resulting solution was cooled in an ice bath. 2,2′-Thiodiethanol (1.17 mmol, 117 μL) was dissolved in 360 μL of EtOH, and this solution was added slowly (over ∼4 h, 10 μL per addition) to the Au(III) solution.…”

“…The ZnF formation was confirmed by circular dichroism (CD) spectroscopy and MS, where the overall CD profile and species distribution in MS were in agreement with data previously reported in both cases. 17,20,21 Ligand Scrambling Evaluation. 31 P NMR Spectroscopy.…”

“…16 The coordination preferences of linear Au(I) in the cysteine-rich environments of both these individual zinc fingers have been probed by traveling-wave ion mobility mass spectrometry, and conformational isomers have been identified. 17 The properties of [AuCl(PR 3 )] can be further modified by varying the phosphine for both steric and electronic effects. Phosphines and carbenes are particularly well suited as carrier ligands when designing Au(I) complexes, as they form stable and strong bonds with Au(I) and the formed Au(I) complexes retain good air and moisture stability.…”

Metabolic Fingerprinting on a Plasmonic Gold Chip for Mass Spectrometry Based in Vitro Diagnostics

“…Notably, there were Ag + adducted molecular peaks using silver nanoshells, since silver ions can afford the ion–dipole interaction with polar functional groups like hydroxyl group in metabolites 45 , 46 and also cationize molecules containing π-bonds. 47 , 48 For comparison, Au + adducted molecular peaks can be found for molecules (e.g., peptides) containing thiol groups, 49 , 50 owing to the strong Au–S chemoaffinity. In this work, the small metabolites as detected did not contain thiol groups, and we observed no Au + adducted molecular peaks, similar to previous literature reports.…”