Mass Determination of Entire Amyloid Fibrils by Using Mass Spectrometry

Electrostatic Linear Ion Trap Optimization Strategy for High Resolution Charge Detection Mass Spectrometry

Single ion mass measurements allow mass distributions to be recorded for heterogeneous samples that cannot be analyzed by conventional mass spectrometry. In charge detection mass spectrometry (CD-MS), ions are detected using a conducting cylinder coupled to a charge sensitive amplifier. For optimum performance, the detection cylinder is embedded in an electrostatic linear ion trap (ELIT) where trapped ions oscillate between end-caps that act as opposing ion mirrors. The oscillating ions generate a periodic signal that is analyzed by fast Fourier transforms. The frequency yields the m/z, and the magnitude provides the charge. With a charge precision of 0.2 elementary charges, ions can be assigned to their correct charge states with a low error rate, and the m/z resolving power determines the mass resolving power. Previously, the best mass resolving power achieved with CD-MS was 300. We have recently increased the mass resolving power to 700, through the better optimization of the end-cap potentials. To make a more dramatic improvement in the m/z resolving power, it is necessary to find an ELIT geometry and end-cap potentials that can simultaneously make the ion oscillation frequency independent of both the ion energy and ion trajectory (angular divergence and radial offset) of the entering ion. We describe an optimization strategy that allows these conditions to be met while also adjusting the signal duty cycle to 50% to maximize the signal-to-noise ratio for the charge measurement. The optimized ELIT provides an m/z resolving power of over 300 000 in simulations. Coupled with the high precision charge determination available with CD-MS, this will yield a mass resolving power of 300 000. Such a high mass resolving power will be transformative for the analysis of heterogeneous samples.

Native Mass Spectrometry: Recent Progress and Remaining Challenges

Native mass spectrometry (nMS) has emerged as an important tool in studying the structure and function of macromolecules and their complexes in the gas phase. In this review, we cover recent advances in nMS and related techniques including sample preparation, instrumentation, activation methods, and data analysis software. These advances have enabled nMS-based techniques to address a variety of challenging questions in structural biology. The second half of this review highlights recent applications of these technologies and surveys the classes of complexes that can be studied with nMS. Complementarity of nMS to existing structural biology techniques and current challenges in nMS are also addressed.

Applications of Charge Detection Mass Spectrometry in Molecular Biology and Biotechnology

Charge detection mass spectrometry (CDMS) is a single-particle technique where the masses of individual ions are determined from simultaneous measurement of their mass-to-charge ratio (m/z) and charge. Masses are determined for thousands of individual ions, and then the results are binned to give a mass spectrum. Using this approach, accurate mass distributions can be measured for heterogeneous and high-molecular-weight samples that are usually not amenable to analysis by conventional mass spectrometry. Recent applications include heavily glycosylated proteins, protein complexes, protein aggregates such as amyloid fibers, infectious viruses, gene therapies, vaccines, and vesicles such as exosomes.

Atmospheric Pressure Mass Spectrometry of Single Viruses and Nanoparticles by Nanoelectromechanical Systems

Mass spectrometry of intact nanoparticles and viruses can serve as a potent characterization tool for material science and biophysics. Inaccessible by widespread commercial techniques, the mass of single nanoparticles and viruses (>10MDa) can be readily measured by nanoelectromechanical systems (NEMS)-based mass spectrometry, where charged and isolated analyte particles are generated by electrospray ionization (ESI) in air and transported onto the NEMS resonator for capture and detection. However, the applicability of NEMS as a practical solution is hindered by their miniscule surface area, which results in poor limit-of-detection and low capture efficiency values. Another hindrance is the necessity to house the NEMS inside complex vacuum systems, which is required in part to focus analytes toward the miniscule detection surface of the NEMS. Here, we overcome both limitations by integrating an ion lens onto the NEMS chip. The ion lens is composed of a polymer layer, which charges up by receiving part of the ions incoming from the ESI tip and consequently starts to focus the analytes toward an open window aligned with the active area of the NEMS electrostatically. With this integrated system, we have detected the mass of gold and polystyrene nanoparticles under ambient conditions and with two orders-of-magnitude improvement in capture efficiency compared to the state-of-the-art. We then applied this technology to obtain the mass spectrum of SARS-CoV-2 and BoHV-1 virions. With the increase in analytical throughput, the simplicity of the overall setup, and the operation capability under ambient conditions, the technique demonstrates that NEMS mass spectrometry can be deployed for mass detection of engineered nanoparticles and biological samples efficiently.

The Role of Rotational Motion in Diffusion NMR Experiments on Supramolecular Assemblies: Application to Sup35NM Fibrils

Pulsed-field gradient (PFG) NMR is an important tool for characterization of biomolecules and supramolecular assemblies. However, for micrometer-sized objects, such as amyloid fibrils, these experiments become difficult to interpret because in addition to translational diffusion they are also sensitive to rotational diffusion. We have constructed a mathematical theory describing the outcome of PFG NMR experiments on rod-like fibrils. To test its validity, we have studied the fibrils formed by Sup35NM segment of the prion protein Sup35. The interpretation of the PFG NMR data in this system is fully consistent with the evidence from electron microscopy. Contrary to some previously expressed views, the signals originating from disordered regions in the fibrils can be readily differentiated from the similar signals representing small soluble species (e.g. proteolytic fragments). This paves the way for diffusion-sorted NMR experiments on complex amyloidogenic samples.

Mass and charge distributions of amyloid fibers involved in neurodegenerative diseases: mapping heterogeneity and polymorphism

Heterogeneity and polymorphism are generic features of amyloid fibers with some important effects on the related disease development. We report here the characterization, by charge detection mass spectrometry, of amyloid fibers made of three polypeptides involved in neurodegenerative diseases: Aβ1-42 peptide, tau and α-synuclein. Beside the mass of individual fibers, this technique enables to characterize the heterogeneity and the polymorphism of the population. In the case of Aβ1-42 peptide and tau protein, several coexisting species could be distinguished and characterized. In the case of α-synuclein, we show how the polymorphism affects the mass and charge distributions.

Simultaneous IR-Spectroscopic Observation of α-Synuclein, Lipids, and Solvent Reveals an Alternative Membrane-Induced Oligomerization Pathway

The intrinsically disordered protein α-synuclein (αS), a known pathogenic factor for Parkinson's disease, can adopt defined secondary structures when interacting with membranes or during fibrillation. The αS-lipid interaction and the implications of this process for aggregation and damage to membranes are still poorly understood. Therefore, we established a label-free infrared (IR) spectroscopic approach to allow simultaneous monitoring of αS conformation and membrane integrity. IR showed its unique sensitivity for identifying distinct β-structured aggregates. A comparative study of wild-type αS and the naturally occurring splicing variant αS Δexon3 yielded new insights into the membrane's capability for altering aggregation pathways.

Charge detection mass spectrometry: weighing heavier things

Charge detection mass spectrometry (CDMS) is a single molecule method where the mass of each ion is directly determined from individual measurements of its mass-to-charge ratio and charge.