The molecular basis of immunosuppression by soluble CD52 is defined by interactions of N-linked and O-linked glycans with HMGB1 box B.

Human soluble CD52 is a short glycopeptide comprising 12 amino acids (GQNDTSQTSSPS) which functions as an immune regulator by sequestering the pro-inflammatory high mobility group box protein 1 (HMGB1) and suppressing immune responses. Recombinant CD52 has been shown to act as a broad anti-inflammatory agent, dampening both adaptive and innate immune responses. This short glycopeptide is heavily glycosylated, with a complex sialylated N-linked glycan at N3 and reported O-linked glycosylation possible on several serine and threonine residues.

Exploring Top-Down Mass Spectrometric Approaches To Probe Forest Cobra () Venom Proteoforms.

Snake venoms are comprised of bioactive proteins and peptides that facilitate severe snakebite envenomation symptoms. A comprehensive understanding of venom compositions and the subtle heterogeneity therein is important. While bottom-up proteomics has been the well-established approach to catalogue venom compositions, top-down proteomics has emerged as a complementary strategy to characterize venom heterogeneity at the intact protein level.

Are Internal Fragments Observable in Electron Based Top-Down Mass Spectrometry?

Protein tandem mass spectrometry (MS/MS) often generates sequence-informative fragments from backbone bond cleavages near the termini. This lack of fragmentation in the protein interior is particularly apparent in native top-down mass spectrometry (MS). Improved sequence coverage, critical for reliable annotation of posttranslational modifications and sequence variants, may be obtained from internal fragments generated by multiple backbone cleavage events.

Characterization of Molecular Tweezer Binding on α-Synuclein with Native Top-Down Mass Spectrometry and Ion Mobility-Mass Spectrometry Reveals a Mechanism for Aggregation Inhibition.

Parkinson's disease, a neurodegenerative disease that affects 15 million people worldwide, is characterized by deposition of α-synuclein into Lewy Bodies in brain neurons. Although this disease is prevalent worldwide, a therapy or cure has yet to be found. Several small compounds have been reported to disrupt fibril formation.

Top-down mass spectrometry and assigning internal fragments for determining disulfide bond positions in proteins.

Disulfide bonds in proteins have a substantial impact on protein structure, stability, and biological activity. Localizing disulfide bonds is critical for understanding protein folding and higher-order structure. Conventional top-down mass spectrometry (TD-MS), where only terminal fragments are assigned for disulfide-intact proteins, can access disulfide information, but suffers from low fragmentation efficiency, thereby limiting sequence coverage.

On the Mechanism of Theta Capillary Nanoelectrospray Ionization for the Formation of Highly Charged Protein Ions Directly from Native Solutions.

Theta capillary nanoelectrospray ionization (θ-nanoESI) can be used to "supercharge" protein ions directly from solution for detection by mass spectrometry (MS). In native top-down MS, the extent of protein charging is low. Given that ions with more charge fragment more readily, increasing charge can enhance the extent of sequence information obtained by top-down MS.

Towards understanding the formation of internal fragments generated by collisionally activated dissociation for top-down mass spectrometry.

Top-down mass spectrometry (TD-MS) generates fragment ions that returns information on the polypeptide amino acid sequence. In addition to terminal fragments, internal fragments that result from multiple cleavage events can also be formed. Traditionally, internal fragments are largely ignored due to a lack of available software to reliably assign them, mainly caused by a poor understanding of their formation mechanism.

Characterization of protein-ligand binding interactions of enoyl-ACP reductase (FabI) by native MS reveals allosteric effects of coenzymes and the inhibitor triclosan.

The enzyme enoyl-ACP reductase (also called FabI in bacteria) is an essential member of the fatty acid synthase II pathway in plants and bacteria. This enzyme is the target of the antibacterial drug triclosan and has been the subject of extensive studies for the past 20 years. Despite the large number of reports describing the biochemistry of this enzyme, there have been no studies that provided direct observation of the protein and its various ligands.

Internal Fragments Generated from Different Top-Down Mass Spectrometry Fragmentation Methods Extend Protein Sequence Coverage.

Top-down mass spectrometry (TD-MS) of intact proteins results in fragment ions that can be correlated to the protein primary sequence. Fragments generated can either be terminal fragments that contain the N- or C-terminus or internal fragments that contain neither termini. Traditionally in TD-MS experiments, the generation of internal fragments has been avoided because of ambiguity in assigning these fragments.

ClipsMS: An Algorithm for Analyzing Internal Fragments Resulting from Top-Down Mass Spectrometry.

Top-down mass spectrometry (TD-MS) of peptides and proteins results in product ions that can be correlated to polypeptide sequence. Fragments can either be terminal fragments, which contain either the N- or the C-terminus, or internal fragments that contain neither termini. Normally, only terminal fragments are assigned due to the computational difficulties of assigning internal fragments.

Naked Mole-Rat, a Rodent with an Apolipoprotein A-I Dimer.

A variety of rodents have been used as experimental animals in metabolic studies of plasma lipids and lipoproteins. These studies have included understanding the functional role of apolipoprotein A-I, the major protein on the surface of HDL. Reviewing the genomic database for entries for rodent apoA-I genes, it was discovered that the naked mole-rat (Heterocephalus glaber) gene encoded a protein with a cysteine at residue 28.

Internal Fragments Generated by Electron Ionization Dissociation Enhance Protein Top-Down Mass Spectrometry.

Top-down proteomics by mass spectrometry (MS) involves the mass measurement of an intact protein followed by subsequent activation of the protein to generate product ions. Electron-based fragmentation methods like electron capture dissociation and electron transfer dissociation are widely used for these types of analyses. Recently, electron ionization dissociation (EID), which utilizes higher energy electrons (>20 eV) has been suggested to be more efficient for top-down protein fragmentation compared to other electron-based dissociation methods.

On the mechanism of protein supercharging in electrospray ionisation mass spectrometry: Effects on charging of additives with short- and long-chain alkyl constituents with carbonate and sulphite terminal groups.

Small organic molecules are used as solution additives in electrospray ionisation mass spectrometry (ESI-MS) to increase the charge states of protein ions and improve the performance of intact protein analysis by tandem mass spectrometry. The properties of the additives that are responsible for their charge-enhancing effects ( dipole moment, gas-phase basicity, Brønsted basicity, and surface tension) have been debated in the literature. We report a series of solution additives for ESI-MS based on cyclic alkyl carbonates and sulphites that have alkyl chains that are from two to ten methylene units long.

Supercharging protein ions in native mass spectrometry using theta capillary nanoelectrospray ionization mass spectrometry and cyclic alkylcarbonates.

Theta nanoelectrospray ionization of protein ions formed from aqueous buffer solutions that are mixed with denaturing solutions containing cyclic alkylcarbonates (e.g., vinyl ethylene carbonate; VEC) results in a significant increase in the extent of ion charging compared to native mass spectrometry.

Extended Protein Ions Are Formed by the Chain Ejection Model in Chemical Supercharging Electrospray Ionization.

Supercharging electrospray ionization can be a powerful tool for increasing charge states in mass spectra and generating unfolded ion structures, yet key details of its mechanism remain unclear. The structures of highly extended protein ions and the mechanism of supercharging were investigated using ion mobility-mass spectrometry. Head-to-tail-linked polyubiquitins (Ubq) were used to determine size and charge state scaling laws for unfolded protein ions formed by supercharging while eliminating amino acid composition as a potential confounding factor.

Extremely supercharged proteins in mass spectrometry: profiling the pH of electrospray generated droplets, narrowing charge state distributions, and increasing ion fragmentation.

The effects of 12 acids, 4 solvents, and 8 low-volatility additives that increase analyte charging (i.e., superchargers) on the charge state distributions (CSDs) of protein ions in ESI-MS were investigated.