Laser-Induced Denaturation of Cytochrome in Electrospray Droplets.

Structural transitions of the model system cytochrome (Cyt ) were monitored by ion mobility spectrometry (IMS) and mass spectrometry (MS) paired with two methods to heat proteins: a variable-temperature electrospray ionization (vT-ESI) source to heat the bulk protein solution and a 10.6 μm CO laser to rapidly heat ESI droplets containing the protein. Previous evidence from our group suggests that information about time-dependent protein structural transitions can be accessed by irradiating protein droplets of different sizes.

A Direct Measurement of the Absolute Energies of Protonated Gly-Pro-Gly-Gly Conformations Using Ion Mobility Spectrometry and Guided Ion Beam Tandem Mass Spectrometry.

Threshold collision-induced dissociation of conformations selected by ion mobility spectrometry is described as a method to determine their absolute relative energies. Here, the method is demonstrated with the cis and trans conformers of the protonated tetrapeptide, Gly-Pro-Gly-Gly, which differ in the orientation of the peptide bond at the proline residue. The trans conformation was found to be more stable than the cis conformation by 4.

A Robust and Automated Platform for Charge Detection Mass Spectrometry of Megadalton Biotherapeutics.

Gene therapies based on adeno-associated viruses are an emerging area with high potential to improve human health. Current quality control techniques to assess contaminates and byproducts from the adeno-associated virus (AAV) production pipelines are lacking in robustness and throughput. To address these limitations, we coupled an automated microfluidic device called SampleStream with Orbitrap-based charge detection mass spectrometry (SS-CDMS).

Diastereomer Characterization of PS-Modified Synthetic Oligonucleotides Using Cyclic IMS-MS.

Synthetic oligonucleotides have emerged as effective therapeutics that regulate gene expression to treat and prevent diseases. Oligonucleotide therapeutics are often modified with a substitution of a phosphorothioate (PS) linkage along the phosphodiester backbone to improve the drug performance and stability. The PS modification creates a mixture of diastereomer structures, increasing by a factor of 2 where is the number of PS linkages.

Variation of CI-2 Conformers upon Addition of Methanol to Water: An IMS-MS-Based Thermodynamic Analysis.

Chymotrypsin inhibitor 2 (CI-2) is a well-studied, textbook example of a cooperative, two-state, native ↔ denatured folding transition. A recent hybrid ion mobility spectrometry (IMS)/mass spectrometry (MS) thermal denaturation study of CI-2 (the well-studied truncated 64-residue model) in water reported evidence that this two-state transition involves numerous (∼41) unique native and non-native (denatured) solution conformations. The characterization of so many, often low-abundance, states is possible because of the very high dynamic range of IMS-MS measurements of ionic species that are produced upon electrospraying CI-2 solutions from a variable temperature electrospray ionization source.

Diketopiperazine Formation from FPGK ( = 1-9) Peptides: Rates of Structural Rearrangements and Mechanisms.

Peptides with penultimate proline residues undergo isomerization of the Phe-Pro peptide bond followed by spontaneous bond cleavage at the Pro-Xxx bond (where Xxx is another amino acid residue), leading to cleavage of the Pro-Xxx bond and formation of a diketopiperazine (DKP). In this paper, ion mobility spectrometry and mass spectrometry techniques were used to study the dissociation kinetics of nine peptides [Phe-Pro-Gly-Lys ( = 1-9)] in ethanol. Shorter ( = 1-3) peptides are found to be more stable than longer ( = 4-9) peptides.

Protons Are Fast and Smart; Proteins Are Slow and Dumb: On the Relationship of Electrospray Ionization Charge States and Conformations.

We present simple considerations of how differences in time scales of motions of protons, the lightest and fastest chemical moiety, and the much longer time scales associated with the dynamics of proteins, among the heaviest and slowest analytes, may allow many protein conformations from solution to be kinetically trapped during the process of electrospraying protein solutions into the gas phase. In solution, the quantum nature of protons leads them to change locations by tunneling, an instantaneous process; moreover, the Grotthuss mechanism suggests that these small particles can respond nearly instantaneously to the dynamic motions of proteins that occur on much longer time scales. A conformational change is accompanied by favorable or unfavorable variations in the free energy of the system, providing the impetus for solvent ↔ protein proton exchange.

Thermal Analysis of a Mixture of Ribosomal Proteins by vT-ESI-MS: Toward a Parallel Approach for Characterizing the .

The thermal stabilities of endogenous, intact proteins and protein assemblies in complex mixtures were characterized in parallel by means of variable-temperature electrospray ionization coupled to mass spectrometry (vT-ESI-MS). The method is demonstrated by directly measuring the melting transitions of seven proteins from a mixture of proteins derived from ribosomes. A proof-of-concept measurement of a fraction of an lysate is provided to extend this approach to characterize the thermal stability of a proteome.

Solid-state packing dictates the unexpected solubility of aromatic peptides.

The understanding and prediction of the solubility of biomolecules, even of the simplest ones, reflect an open question and unmet need. Short aromatic tripeptides are among the most highly aggregative biomolecules. However, in marked contrast, Ala-Phe-Ala (AFA) was surprisingly found to be non-aggregative and could be solubilized at millimolar concentrations.

Heterogeneity of Glycan Processing on Trimeric SARS-CoV-2 Spike Protein Revealed by Charge Detection Mass Spectrometry.

The heterogeneity associated with glycosylation of the 66 N-glycan sites on the protein trimer making up the spike (S) region of the SARS-CoV-2 virus has been assessed by charge detection mass spectrometry (CDMS). CDMS allows simultaneous measurement of the mass-to-charge ratio and charge of individual ions, so that mass distributions can be determined for highly heterogeneous proteins such as the heavily glycosylated S protein trimer. The CDMS results are compared to recent glycoproteomics studies of the structure and abundance of glycans at specific sites.

Evidence for Many Unique Solution Structures for Chymotrypsin Inhibitor 2: A Thermodynamic Perspective Derived from vT-ESI-IMS-MS Measurements.

Chymotrypsin inhibitor 2 (CI-2) is a classic model for two-state cooperative protein folding and is one of the most extensively studied systems. Alan Fersht, a pioneer in the field of structural biology, has studied the wild-type (wt) and over 100 mutant forms of CI-2 with traditional analytical and biochemical techniques. Here, we examine wt CI-2 and three mutant forms (A16G, K11A, L32A) to demonstrate the utility of variable-temperature (vT) electrospray ionization (ESI) paired with ion mobility spectrometry (IMS) and mass spectrometry (MS) to map the free energy folding landscape.

Understanding the Thermal Denaturation of Myoglobin with IMS-MS: Evidence for Multiple Stable Structures and Trapped Pre-equilibrium States.

Thermal denaturation of holomyoglobin (hMb) in solution (10 mM ammonium acetate at pH = 4.5, 6.8, and 9.

Melting of Hemoglobin in Native Solutions as measured by IMS-MS.

Thermally induced structural transitions of the quaternary structure of the hemoglobin tetramer (human) in aqueous solution (150 mM ammonium acetate) were investigated using a variable temperature electrospray ionization (vt-ESI) technique in combination with ion mobility spectrometry (IMS) and mass spectrometry (MS) measurements. At low solution temperatures (28 to ∼40 °C), a heterotetrameric (αβ) complex is the most abundant species that is observed. When the solution temperature is increased, this assembly dissociates into heterodimers (holo αβ forms) before ultimately forming insoluble aggregates at higher temperatures (>60 °C).

Determination of Gas-Phase Ion Structures of Locally Polar Homopolymers Through High-Resolution Ion Mobility Spectrometry-Mass Spectrometry.

The strong synergy arising from coupling two orthogonal analytical techniques such as ion mobility and mass spectrometry can be used to separate complex mixtures and determine structural information of analytes in the gas phase. A tandem study is performed using two systems with different gases and pressures to ascertain gas-phase conformations of homopolymer ions. Aside from spherical and stretched configurations, intermediate configurations formed by a multiply charged globule and a "bead-on-a-string" appendix are confirmed for polyethylene-glycol (PEG), polycaprolactone (PCL), and polydimethylsiloxane (PDMS).

Melting proteins confined in nanodroplets with 10.6 μm light provides clues about early steps of denaturation.

Ubiquitin confined within nanodroplets was irradiated with a variable-power CO2 laser. Mass spectrometry analysis shows evidence for a protein "melting"-like transition within droplets prior to solvent evaporation and ion formation. Ion mobility spectrometry reveals that structures associated with early steps of denaturation are trapped because of short droplet lifetimes.

Melting Proteins: Evidence for Multiple Stable Structures upon Thermal Denaturation of Native Ubiquitin from Ion Mobility Spectrometry-Mass Spectrometry Measurements.

Ion mobility and mass spectrometry techniques are coupled with a temperature-controlled electrospray ionization source to follow the structural transitions of ubiquitin in aqueous solution (pH = 3) at elevated solution temperatures (T = 26-96 °C). Changes in the charge state distribution are consistent with a two-state, cooperative unfolding transition having a melting temperature of T = 71 ± 2 °C, in agreement with prior measurements [ Wintrode , P. L.

On-line chiral analysis using the kinetic method.

Chiral analysis of constituents in solution-phase reaction mixtures can be performed by tandem mass spectrometry using the kinetic method to determine the enantiomeric excess (ee). Simply diluting an aliquot of a reaction mixture, adjusting the pH, and adding reagents necessary to form a chiral cluster ion allows chiral analysis. The product of a stereospecific N-selective alkylation reaction, 2-(3-(2-methoxyethoxy)-5-oxo-1,6-naphthyridin-6(5H)-yl)propanoic acid, was monitored for ee during the course of reaction, and it showed the expected inversion without ee erosion.