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Structural characterization of intrinsically disordered proteins (IDPs) has been a major challenge in the field of protein science due to limited capabilities to obtain full-length high-resolution structures. Native ESI-MS with top-down MS was utilized to obtain structural features of protein-ligand binding for the Parkinson's disease-related protein, α-synuclein (αSyn), which is natively unstructured. Binding of heavy metals has been implicated in the accelerated formation of αSyn aggregation. Using high-resolution Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry, native top-down MS with various fragmentation methods, including electron capture dissociation (ECD), collisional activated dissociation (CAD), and multistage tandem MS (MS3), deduced the binding sites of cobalt and manganese to the C-terminal region of the protein. Ion mobility MS (IM-MS) revealed a collapse toward compacted states of αSyn upon metal binding. The combination of native top-down MS and IM-MS provides structural information of protein-ligand interactions for intrinsically disordered proteins. Graphical Abstract ᅟ.

In tauopathy conditions, such as Alzheimer's disease (AD), highly soluble and natively unfolded tau polymerizes into an insoluble filament; however, the mechanistic details of this process remain unclear. In the brains of AD patients, only a minor segment of tau forms β-helix-stacked protofilaments, while its flanking regions form disordered fuzzy coats. Here, it is demonstrated that the tau AD nucleation core (tau-AC) sufficiently induced self-aggregation and recruited full-length tau to filaments. Unexpectedly, phospho-mimetic forms of tau-AC (at Ser324 or Ser356) show markedly reduced oligomerization and seeding propensities. Biophysical analysis reveal that the N-terminus of tau-AC facilitates the fibrillization kinetics as a nucleation motif, which becomes sterically shielded through phosphorylation-induced conformational changes in tau-AC. Tau-AC oligomers are efficiently internalized into cells via endocytosis and induced endogenous tau aggregation. In primary hippocampal neurons, tau-AC impaired axon initial segment plasticity upon chronic depolarization and is mislocalized to the somatodendritic compartments. Furthermore, it is observed significantly impaired memory retrieval in mice intrahippocampally injected with tau-AC fibrils, which corresponds to the neuropathological staining and neuronal loss in the brain. These findings identify tau-AC species as a key neuropathological driver in AD, suggesting novel strategies for therapeutic intervention. [ABSTRACT FROM AUTHOR]

A number of phosphatidylcholine (PC) cations spanning a mass range of 400-1000 Da are investigated using electrospray ionization mass spectrometry coupled with traveling wave ion mobility spectrometry (TWIMS). A high correlation between mass and mobility is demonstrated with saturated phosphatidylcholine cations in [N.sub.2]. A significant deviation from this mass--mobility correlation line is observed for the unsaturated PC cation. We found that the double bond in the acyl chain causes a 5% reduction in drift time. The drift time is reduced at a rate of ~1% for each additional double bond. Theoretical collision cross sections of PC cations exhibit good agreement with experimentally evaluated values. Collision cross sections are determined using the recently derived relationship between mobility and drift time in TWIMS stacked ring ion guide (SRIG) and compared to estimated collision cross sections using an empiric calibration method. Computational analysis was performed using the modified trajectory (TJ) method with nonspherical [N.sub.2] molecules as the drift gas. The difference between estimated collision cross sections and theoretical collision cross sections of PC cations is related to the sensitivity of the PC cation collision cross sections to the details of the ion--neutral interactions. The origin of the observed correlation and deviation between mass and mobility of PC cations is discussed in terms of the structural rigidity of these molecules using molecular dynamic simulations. 10.1021/ac900672a

A number of tertiary amine and quaternary ammonium cations spanning a mass range of 60-146 amu (trimethylamine, tetramethylammonium, trimethylethylammonium, N,N-dimethylaminoethanoi, choline, N, N-dimethylglycine, betaine, acetylcholine, (3-carboxypropyl)trimethylammonium) were investgated using electrospray ionization ion mobility spectrometry. Measured ion mobilities demonstrate a high correlation between mass and mobility in [N.sub.2]. In addition, identical mobilities within experimental uncertainties are observed for structurally dissimilar ions with similar ion masses. For example, dimethylethylammonium (88 amu) cations and protonated N, N-dimethylaminoethanol cations (90 amu) show identical mobilities (1.93 [cm.sup.2] [V.sup.-1] [s.sup.-1]) though N,Ndimethylaminoethanol contains a hydroxyl functional group while dimethylethylammonium only contains alkyl groups. Computational analysis was performed using the modified trajectory (TJ) method with nonspherical [N.sub.2] molecules as the drift gas. The sensitivity of the ammonium cation collision cross sections to the details of the ion-neutral interactions was investigated and compared to other classes of organic molecules (carboxylic acids and abiotic amino acids). The specific charge distribution of the molecular ions in the investigated mass range has an insignificant affect on the collision cross section.

A new method is described for identifying disulfide linkages in peptides by using mass spectrometry. Collisional activation of singly charged cationic alkali and alkaline earth metal complexes has resulted in the highly selective elimination of hydrogen disulfide.

A number of carboxylate anions spanning a mass range of 87-253 amu were investigated using electroscopy ionization ion mobility spectroscopy. The carboxylate anions that form ring confirmations generally show higher ion mobility values than those that form extended conformations.

Reduced ion mobilities in 14 aboitic amino acids were determined using the electrospray ionization ion mobility spectrometry in N2 and CO2 drift gases. This model was primarily used to understand the protonated amino acid mass mobility correlation.