3 research outputs found
Specific and Efficient N‑Propionylation of Histones with Propionic Acid <i>N</i>‑Hydroxysuccinimide Ester for Histone Marks Characterization by LC-MS
Histones participate in epigenetic regulation via a variety
of
dynamic posttranslational modifications (PTMs) on them. Mass spectrometry
(MS) has become a powerful tool to investigate histone PTMs. With
the bottom-up mass spectrometry approach, chemical derivatization
of histones with propionic anhydride or deuterated acetic anhydride
followed by trypsin digestion was widely used to block the hydrophilic
lysine residues and generate compatible peptides for LC-MS analysis.
However, certain severe side reactions (such as acylation on tyrosine
or serine) caused by acid anhydrides will lead to a number of analytical
issues such as reducing results accuracy and impairing the reproducibility
and sensitivity of MS analysis. As an alternative approach, we report
a novel derivatization method that utilizes <i>N</i>-hydroxysuccinimide
ester to specifically and efficiently derivatize both free and monomethylated
amine groups in histones. A competitive inhibiting strategy was implemented
in our method to effectively prevent the side reactions. We demonstrated
that our method can achieve excellent specificity and efficiency for
histones derivatization in a reproducible manner. Using this derivatization
method, we succeeded to quantitatively profile the histone PTMs in
KMS11 cell line with selective knock out of translocated NSD2 allele
(TKO) and the original parental KMS11 cell lines (PAR) (NSD2, a histone
methyltransferase that catalyzes the histone H3 K36 methylation),
which revealed a significant crosstalk between H3 protein K27 methylation
and adjacent K36 methylation
Tyrosine-Directed Conjugation of Large Glycans to Proteins via Copper-Free Click Chemistry
We have demonstrated that the insertion
of alkyne-containing bifunctional
linkers into the tyrosine residues of the carrier protein, followed
by the copper mediated azide–alkyne [3 + 2] cycloaddition of
carbohydrates, is a robust approach for the preparation of glycoconjugates
with defined glycans, carrier, and connectivity. Conjugation of Group
B Streptococcus (GBS) capsular polysaccharides
to streptococcal pilus protein could extend the vaccine coverage to
a variety of strains. Application of our protocol to these large charged
polysaccharides occurred at low yields. Herein we developed a tyrosine-directed
conjugation approach based on the copper-free click chemistry of sugars
modified with cyclooctynes, which enables efficient condensation of
synthetic carbohydrates. Most importantly, this strategy was demonstrated
to be more effective than the corresponding copper catalyzed reaction
for the insertion of GBS onto the tyrosine residues of GBS pilus proteins,
previously selected as vaccine antigens through the so-called <i>reverse vaccinology</i>. Integrity of protein epitopes in the
modified proteins was ascertained by competitive ELISA, and conjugation
of polysaccharide to protein was confirmed by SDS page electrophoresis
and immunoblot assays. The amount of conjugated polysaccharide was
estimated by high-performance anion-exchange chromatography coupled
with pulsed amperometric detection (HPAEC-PAD). The described technology
is particularly suitable for proteins used with the dual role of vaccine
antigen and carrier for the carbohydrate haptens
Absolute Quantification of Histone PTM Marks by MRM-Based LC-MS/MS
The N-terminal tails of core histones
harbor the sites of numerous
post-translational modifications (PTMs) with important roles in the
regulation of chromatin structure and function. Profiling histone
PTM marks provides data that help understand the epigenetics events
in cells and their connections with cancer and other diseases. Our
previous study demonstrated that specific derivatization of histone
peptides by NHS propionate significantly improved their chromatographic
performance on reversed phase columns for LC/MS analysis. As a step
forward, we recently developed a multiple reaction monitoring (MRM)
based LC-MS/MS method to analyze 42 targeted histone peptides. By
using stable isotopic labeled peptides as internal standards that
are spiked into the reconstituted solutions, this method allows to
measure absolute concentration of the tryptic peptides of H3 histone
proteins extracted from cancer cell lines. The method was thoroughly
validated for the accuracy and reproducibility through analyzing recombinant
histone proteins and cellular samples. The linear dynamic range of
the MRM assays was achieved in 3 orders of magnitude from 1 nM to
1 ÎĽM for all targeted peptides. Excellent intrabatch and interbatch
reproducibility (<15% CV) was obtained. This method has been used
to study translocated NSD2 (a histone lysine methyltransferase that
catalyzes the histone lysine 36 methylation) function with its overexpression
in KMS11 multiple myeloma cells. From the results we have successfully
quantitated both individual and combinatorial histone marks in parental
and NSD2 selective knockout KMS11 cells