57 research outputs found
Native Proteomics in Discovery Mode Using Size-Exclusion Chromatography–Capillary Zone Electrophoresis–Tandem Mass Spectrometry
Native proteomics aims to characterize complex proteomes under native conditions and
ultimately produces a full picture of endogenous protein complexes in cells. It requires
novel analytical platforms for high-resolution and liquid-phase separation of protein
complexes prior to native mass spectrometry (MS) and MS/MS. In this work, size
exclusion chromatography (SEC)-capillary zone electrophoresis (CZE)-MS/MS was
developed for native proteomics in discovery mode, resulting in the identification of 144
proteins, 672 proteoforms, and 23 protein complexes from the Escherichia coli
proteome. The protein complexes include four protein homodimers, 16 protein-metal
complexes, two protein-[2Fe-2S] complexes, and one protein-glutamine complex. Half
of them have not been reported in the literature. This work represents the first example
of online liquid-phase separation-MS/MS for characterization of a complex proteome
under the native condition, offering the proteomics community an efficient and simple
platform for native proteomics
Integrated Capillary Zone Electrophoresis–Electrospray Ionization Tandem Mass Spectrometry System with an Immobilized Trypsin Microreactor for Online Digestion and Analysis of Picogram Amounts of RAW 264.7 Cell Lysate
A capillary zone electrophoresis
(CZE) electrospray ionization
(ESI) tandem mass spectrometry (MS/MS) system was integrated with
an immobilized trypsin microreactor. The system was evaluated and
then applied for online digestion and analysis of picogram loadings
of RAW 264.7 cell lysate. Protein samples were dissolved in a buffer
containing 50% (v/v) acetonitrile (ACN), and then directly loaded
into the capillary for digestion, followed by CZE separation and MS/MS
identification. The organic solvent (50% (v/v) ACN) assisted the immobilized
trypsin digestion and simplified the protein sample preparation protocol.
Neither protein reduction nor alkylation steps were employed, which
minimized sample loss and contamination. The integrated CZE–ESI-MS/MS
system generated confident identification of bovine serum albumin
(BSA) with 19% sequence coverage and 14 peptide identifications (IDs)
when 20 fmol was loaded. When only 1 fmol of BSA was injected, one
BSA peptide was consistently detected. For the analysis of a standard
protein mixture, the integrated system produced efficient protein
digestion and confident identification for proteins with different
molecular weights and isoelectric points when a low-femtomole amount
was loaded for each protein. We further applied the system for triplicate
analysis of a RAW 264.7 cell lysate; 2 ± 1 and 7 ± 2 protein
groups were confidently identified from only 300 pg and 3 ng loadings,
respectively. The 300 pg sample loading corresponds to the protein
content of three RAW 264.7 cells. In addition to high-sensitivity
analysis, the integrated CZE–ESI-MS/MS system produces good
reproducibility in terms of peptide and protein IDs, peptide migration
time, and peptide intensity
Integrated Capillary Zone Electrophoresis–Electrospray Ionization Tandem Mass Spectrometry System with an Immobilized Trypsin Microreactor for Online Digestion and Analysis of Picogram Amounts of RAW 264.7 Cell Lysate
A capillary zone electrophoresis
(CZE) electrospray ionization
(ESI) tandem mass spectrometry (MS/MS) system was integrated with
an immobilized trypsin microreactor. The system was evaluated and
then applied for online digestion and analysis of picogram loadings
of RAW 264.7 cell lysate. Protein samples were dissolved in a buffer
containing 50% (v/v) acetonitrile (ACN), and then directly loaded
into the capillary for digestion, followed by CZE separation and MS/MS
identification. The organic solvent (50% (v/v) ACN) assisted the immobilized
trypsin digestion and simplified the protein sample preparation protocol.
Neither protein reduction nor alkylation steps were employed, which
minimized sample loss and contamination. The integrated CZE–ESI-MS/MS
system generated confident identification of bovine serum albumin
(BSA) with 19% sequence coverage and 14 peptide identifications (IDs)
when 20 fmol was loaded. When only 1 fmol of BSA was injected, one
BSA peptide was consistently detected. For the analysis of a standard
protein mixture, the integrated system produced efficient protein
digestion and confident identification for proteins with different
molecular weights and isoelectric points when a low-femtomole amount
was loaded for each protein. We further applied the system for triplicate
analysis of a RAW 264.7 cell lysate; 2 ± 1 and 7 ± 2 protein
groups were confidently identified from only 300 pg and 3 ng loadings,
respectively. The 300 pg sample loading corresponds to the protein
content of three RAW 264.7 cells. In addition to high-sensitivity
analysis, the integrated CZE–ESI-MS/MS system produces good
reproducibility in terms of peptide and protein IDs, peptide migration
time, and peptide intensity
Coupling Capillary Zone Electrophoresis to a Q Exactive HF Mass Spectrometer for Top-down Proteomics: 580 Proteoform Identifications from Yeast
We used reversed-phase
liquid chromatography to separate the yeast
proteome into 23 fractions. These fractions were then analyzed using
capillary zone electrophoresis (CZE) coupled to a Q-Exactive HF mass
spectrometer using an electrokinetically pumped sheath flow interface.
The parameters of the mass spectrometer were first optimized for top-down
proteomics using a mixture of seven model proteins; we observed that
intact protein mode with a trapping pressure of 0.2 and normalized
collision energy of 20% produced the highest intact protein signals
and most protein identifications. Then, we applied the optimized parameters
for analysis of the fractionated yeast proteome. From this, 580 proteoforms
and 180 protein groups were identified via database searching of the
MS/MS spectra. This number of proteoform identifications is two times
larger than that of previous CZE-MS/MS studies. An additional 3,243
protein species were detected based on the parent ion spectra. Post-translational
modifications including N-terminal acetylation, signal peptide removal,
and oxidation were identified
Bottom-Up Proteomics of <i>Escherichia coli</i> Using Dynamic pH Junction Preconcentration and Capillary Zone Electrophoresis-Electrospray Ionization-Tandem Mass Spectrometry
We report the use of the dynamic
pH junction based capillary zone
electrophoresis-electrospray ionization-tandem mass spectrometry (CZE-ESI-MS/MS)
for bottom-up proteomics with an electrokinetically pumped sheath-flow
nanospray capillary electrophoresis-mass spectrometry (CE-MS) interface
and both LTQ-XL and LTQ-Orbitrap-Velos mass spectrometers. Conventional
injection of 20 nL of a 1 mg/mL BSA digest identified 37 peptides
and produced 66% sequence coverage. In contrast, pH junction injection
of 130 nL (or larger) of a 0.05 mg/mL BSA digest identified 40 peptides
and produced 70% coverage using a pH 6.5 sample buffer and the LTQ.
A 20 nL conventional injection of a 1 mg/mL <i>Escherichia coli</i> digest identified 508 peptides and 199 proteins with the LTQ. A
400 nL pH junction injection of a 0.1 mg/mL <i>E. coli</i> digest identified 527 peptides and 179 proteins with the LTQ. Triplicate
technical replicates of a 0.01 mg/mL sample with 400-nL injection
volume using a pH junction identified 288 ± 9 peptides and 121
± 5 proteins with the LTQ. There was outstanding concordance
in migration time between the pH junction and normal injection. The
pH junction produced narrower peaks and significant concentration
for all but the most acidic components in the sample. Compared with
the conventional stacking method, the pH junction method can generate
comparable performance for small injection volume (20 nL) and significantly
better concentration performance for a large injection volume (200
nL). We also applied the pH junction to three intact standard proteins
and observed a >10× increase in peak intensity compared to
conventional
injection
Single-Shot Proteomics Using Capillary Zone Electrophoresis–Electrospray Ionization-Tandem Mass Spectrometry with Production of More than 1 250 <i>Escherichia coli</i> Peptide Identifications in a 50 min Separation
Capillary zone electrophoresis (CZE)–electrospray
ionization-tandem
mass spectrometry (ESI-MS/MS) was optimized and applied for analysis
of 1–100 ng <i>Escherichia coli</i> protein digests
in a single run (single-shot analysis). The system employed an electrokinetically
pumped nanospray interface, a coated capillary, and stacking conditions
for sample injection. More than 1 250 peptides were identified
by optimized single-shot CZE–ESI-MS/MS with 100 ng digest loaded
and 50 min analysis time. When 10 ng and 1 ng digests were loaded,
about 1 000 and 600 peptides were identified in a single-shot
analysis, respectively. Compared with single-shot ultraperformance
liquid chromatography (UPLC)–ESI-MS/MS, CZE–ESI-MS/MS
produced fewer peptide IDs (1 377 ± 128 vs 1 875
± 32) for large sample loading amounts (100 ng) with the same
mass spectrometer time (50 min). However, when the loaded digest was
mass limited (1 ng), CZE–ESI-MS/MS generated many more peptide
identifications than UPLC–ESI-MS/MS (627 ± 38 vs 342 ±
113). In addition, CZE–ESI-MS/MS and UPLC–ESI -MS/MS
provided complementary peptide level identifications. These results
suggest that CZE–ESI-MS/MS may be useful for large-scale, comprehensive,
and confident proteomics analysis
Site-Specific Glycan Heterogeneity Characterization by Hydrophilic Interaction Liquid Chromatography Solid-Phase Extraction, Reversed-Phase Liquid Chromatography Fractionation, and Capillary Zone Electrophoresis-Electrospray Ionization-Tandem Mass Spectrometry
Reversed-phase chromatographic
separation of glycopeptides tends
to be dominated by the peptide composition. In contrast, capillary
zone electrophoresis separation of glycopeptides is particularly sensitive
to the sialic acid composition of the glycan. In this paper, we combine
the two techniques to achieve superior N-glycopeptide analysis. Glycopeptides
were first isolated from a tryptic digest using hydrophilic interaction
liquid chromatography (HILIC) solid-phase extraction. The glycopeptides
were separated using reversed-phase ultra high-performance liquid
chromatography (UHPLC) to generate four fractions corresponding to
different peptide backbones. Capillary zone electrophoresis-electrospray
ionization-tandem mass spectrometry (CZE-ESI-MS/MS) was used to analyze
the fractions. We applied this method for the analysis of alpha-1-acid
glycoprotein (AGP). A total of 268 site-specific N-glycopeptides were
detected, representing eight different glycosylation sites from two
isomers of AGP. Glycans included tetra-sialic acids with multi N-acetyllactosamine
(LacNAc) repeats and unusual pentasialylated terminal sialic acids.
Reversed-phase UHPLC coupled with CZE generated ∼35% more N-glycopeptides
than direct reversed-phase UHPLC-ESI-MS/MS analysis and ∼70%
more N-glycopeptides than direct CZE-ESI-MS/MS analysis. This approach
is a promising tool for global, site-specific glycosylation analysis
of highly heterogeneous glycoproteins with mass-limited samples
Capillary Isoelectric Focusing-Tandem Mass Spectrometry and Reversed-Phase Liquid Chromatography-Tandem Mass Spectrometry for Quantitative Proteomic Analysis of Differentiating PC12 Cells By Eight-Plex Isobaric Tags for Relative and Absolute Quantification
We report the application of capillary
isoelectric focusing for
quantitative analysis of a complex proteome. Biological duplicates
were generated from PC12 cells at days 0, 3, 7, and 12 following treatment
with nerve growth factor. These biological duplicates were digested
with trypsin, labeled using eight-plex isobaric tags for relative
and absolute quantification (iTRAQ) chemistry, and pooled. The pooled
peptides were separated into 25 fractions using reversed-phase liquid
chromatography (RPLC). Technical duplicates of each fraction were
separated by capillary isoelectric focusing (cIEF) using a set of
amino acids as ampholytes. The cIEF column was interfaced to an Orbitrap
Velos mass spectrometer with an electrokinetically pumped sheath-flow
nanospray interface. This HPLC-cIEF-electrospray-tandem mass spectrometry
(ESI-MS/MS) approach identified 835 protein groups and produced 2 329
unique peptides IDs. The biological duplicates were analyzed in parallel
using conventional strong-cation exchange (SCX)-RPLC-ESI-MS/MS. The
iTRAQ peptides were first separated into eight fractions using SCX.
Each fraction was then analyzed by RPLC-ESI-MS/MS. The SCX-RPLC approach
generated 1 369 protein groups and 3 494 unique peptide
IDs. For protein quantitation, 96 and 198 differentially expressed
proteins were obtained with RPLC-cIEF and SCX-RPLC, respectively.
The combined set identified 231 proteins. Protein expression changes
measured by RPLC-cEIF and SCX-RPLC were highly correlated
Fast Top-Down Intact Protein Characterization with Capillary Zone Electrophoresis–Electrospray Ionization Tandem Mass Spectrometry
Capillary
zone electrophoresis (CZE)–electrospray ionization
tandem mass spectrometry (ESI-MS/MS) was applied for rapid top-down
intact protein characterization. A mixture containing four model proteins
(cytochrome <i>c</i>, myoglobin, bovine serum albumin (BSA),
and β-casein) was used as the sample. The CZE–ESI-MS
system was first evaluated with the mixture. The four model proteins
and five impurities were baseline-separated within 12 min. The limits
of detection [signal-to-noise ratio (S/N) = 3] of the four model proteins
ranged from 20 (cytochrome <i>c</i>) to 800 amol (BSA).
The relative standard deviations of migration time and intensity for
the four model proteins were less than 3% and 30%, respectively, in
quintuplicate runs. CZE–ESI-MS/MS was then applied for top-down
characterization of the mixture. Three of the model proteins (all
except BSA) and an impurity (bovine transthyretin) were confidently
identified by database searching of the acquired tandem spectra from
protein fragmentation. Modifications including phosphorylation, N-terminal
acetylation, and heme group binding were identified
Capillary Isoelectric Focusing-Tandem Mass Spectrometry and Reversed-Phase Liquid Chromatography-Tandem Mass Spectrometry for Quantitative Proteomic Analysis of Differentiating PC12 Cells By Eight-Plex Isobaric Tags for Relative and Absolute Quantification
We report the application of capillary
isoelectric focusing for
quantitative analysis of a complex proteome. Biological duplicates
were generated from PC12 cells at days 0, 3, 7, and 12 following treatment
with nerve growth factor. These biological duplicates were digested
with trypsin, labeled using eight-plex isobaric tags for relative
and absolute quantification (iTRAQ) chemistry, and pooled. The pooled
peptides were separated into 25 fractions using reversed-phase liquid
chromatography (RPLC). Technical duplicates of each fraction were
separated by capillary isoelectric focusing (cIEF) using a set of
amino acids as ampholytes. The cIEF column was interfaced to an Orbitrap
Velos mass spectrometer with an electrokinetically pumped sheath-flow
nanospray interface. This HPLC-cIEF-electrospray-tandem mass spectrometry
(ESI-MS/MS) approach identified 835 protein groups and produced 2 329
unique peptides IDs. The biological duplicates were analyzed in parallel
using conventional strong-cation exchange (SCX)-RPLC-ESI-MS/MS. The
iTRAQ peptides were first separated into eight fractions using SCX.
Each fraction was then analyzed by RPLC-ESI-MS/MS. The SCX-RPLC approach
generated 1 369 protein groups and 3 494 unique peptide
IDs. For protein quantitation, 96 and 198 differentially expressed
proteins were obtained with RPLC-cIEF and SCX-RPLC, respectively.
The combined set identified 231 proteins. Protein expression changes
measured by RPLC-cEIF and SCX-RPLC were highly correlated
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