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W Andy Tao

Publications and source records attributed to W Andy Tao.

9 recordsLinked to original sources
PubMed2007

A novel quantitative proteomics strategy to study phosphorylation-dependent peptide-protein interactions.

Phosphorylation-dependent protein-protein interactions provide the mechanism for a large number of intracellular signal transduction pathways. One of the goals of signal transduction research is to understand more precisely the nature of these phosphorylation-dependent interactions. Here, we report a novel strategy based on quantitative proteomics that allows for the rapid analysis of peptide-protein interactions with more than one phosphorylation site involved. The phosphorylation of two tyrosine residues, Y342 and Y346, within the linker B region of the protein-tyrosine kinase Syk is important for optimal signaling from the B cell receptor for antigen. We employed four amino-specific, isobaric reagents to differentially label proteins interacting in vitro with four Syk peptides containing none, one, or two phosphates on tyrosine residues Y342 and Y346, respectively. In total, 76 proteins were identified and quantified, 11 of which were dependent on the phosphorylation of individual tyrosine residues. One of the proteins, peroxiredoxin 1, preferably bound to phosphorylated Y346, which was further verified by Western blotting results. Thus, we demonstrate that the use of 4-fold multiplexing allows for relative protein measurements simultaneously for the identification of interacting proteins dependent on the phosphorylation of specific residues.

Algorithms↗
PubMed2005

Quantitative phosphoproteome analysis using a dendrimer conjugation chemistry and tandem mass spectrometry.

We present a robust and general method for the identification and relative quantification of phosphorylation sites in complex protein mixtures. It is based on a new chemical derivatization strategy using a dendrimer as a soluble polymer support and tandem mass spectrometry (MS/MS). In a single step, phosphorylated peptides are covalently conjugated to a dendrimer in a reaction catalyzed by carbodiimide and imidazole. Modified phosphopeptides are released from the dendrimer via acid hydrolysis and analyzed by MS/MS. When coupled with an initial antiphosphotyrosine protein immunoprecipitation step and stable-isotope labeling, in a single experiment, we identified all known tyrosine phosphorylation sites within the immunoreceptor tyrosine-based activation motifs (ITAM) of the T-cell receptor (TCR) CD3 chains, and previously unknown phosphorylation sites on total 97 tyrosine phosphoproteins and their interacting partners in human T cells. The dynamic changes in phosphorylation were quantified in these proteins.

Cells, Cultured↗
PubMed2004

Proteomic analysis identifies that 14-3-3zeta interacts with beta-catenin and facilitates its activation by Akt.

beta-Catenin is a central effector of Wnt signaling in embryonic and stem cell development and in tumorigenesis. Here, through a mass spectrometric analysis of a beta-catenin protein complex, we identified 12 proteins as putative beta-catenin interactors. We show that one of them, 14-3-3zeta, enhances beta-catenin-dependent transcription by maintaining a high level of beta-catenin protein in the cytoplasm. More importantly, 14-3-3zeta facilitates activation of beta-catenin by the survival kinase Akt and colocalizes with activated Akt in intestinal stem cells. We propose that Akt phosphorylates beta-catenin, which results in 14-3-3zeta binding and stabilization of beta-catenin, and these interactions may be involved in stem cell development.

14-3-3 Proteins↗
PubMed2003

Kinetic method for the simultaneous chiral analysis of different amino acids in mixtures.

The kinetic method has been extended to enantiomeric excess (ee) determinations on amino acids present in mixtures. Singly charged trimeric clusters [Cu(II)(ref*)(2)(A(m)) - H](+) are readily generated by electrospraying solutions containing Cu(II), a chiral reference ligand (ref*), and the amino acids (analytes A(m), m = 1-3). A trimeric cluster ion for each amino acid is individually mass-selected and then collisionally activated to cause dissociation by competitive loss of either the reference ligand or the analyte. For each analyte in the mixture, as shown from separate experiments, the logarithm of the ratio of the fragment abundances for the complex containing one enantiomer of this analyte expressed relative to that for the fragments of the corresponding complex containing the other enantiomer is linearly related to the enantiomeric composition of the amino acid. Formation and dissociation of each trimeric complex ion are shown to occur independently of the presence of other analytes. Chiral selectivity appears to be an intrinsic property and the chiral selectivity R(chiral(m)) measured from the mixture of analytes is equal to R(chiral) measured for the pure analyte. The sensitive nature of the methodology and the linear relationship between the logarithm of the fragment ion abundance ratio and the optical purity, characteristic of the kinetic method, allow the determination of chiral impurities of less than 2% ee in individual compounds present in mixtures by simply recording the ratios of fragment ion abundances in a tandem mass spectrum.

Amino Acids↗
PubMed2003

Advances in quantitative proteomics via stable isotope tagging and mass spectrometry.

The high-throughput identification and accurate quantification of proteins are essential components of proteomic strategies for studying cellular functions and processes. Techniques that are largely based on stable isotope protein or peptide labeling and automated tandem mass spectrometry are increasingly being applied in quantitative proteomic studies. Over the past year, significant progress has been made toward improving and diversifying these technologies with respect to the methods for stable isotope labeling, process automation and data processing and analysis. Advances in stable isotope protein labeling and recent biological studies that used stable isotope based quantitative proteomics techniques are reviewed.

Affinity Labels↗
PubMed2002

Quotient ratio method for quantitative enantiomeric determination by mass spectrometry.

The quotient ratio (QR) method, a new quantitative method for enantiomeric determination by mass spectrometry, is presented. The method is illustrated by the case in which a chiral analyte (A) and a chiral reference compound (ref*) are simultaneously coordinated to a transition metal ion (e.g., Cu2+ or Zn2 ) to form a singly charged deprotonated cluster ion in the course of electrospray ionization. The trimeric complex ion (three chiral ligands-2 mol of the analyte and 1 mol of the reference compound) is collisionally activated and undergoes dissociation by competitive loss of either a neutral reference or a neutral analyte. The ratio of the product ion branching ratios measured when pure chiral reference compounds (ref*D and ref*L) are employed in separate experiments is related via the kinetic method to the enantiomeric composition of the chiral mixture. This quotient ratio is logarithmically related to enantiomeric purity. In contrast to the previous single ratio method (Tao, W. A.; Zhang, D.; Wang, F.; Thomas, P. D.; Cooks, R. G. Anal. Chem. 1999, 71, 4427), the QR method reported here requires only one sample of the analyte with known optical purity to allow construction of a calibration curve. Accurate determinations of enantiomeric excess for amino acids and the chiral drug DOPA are demonstrated.

Amino Acids↗
PubMed2002

Ligand and metal-ion effects in metal-ion clusters used for chiral analysis of alpha-hydroxy acids by the kinetic method.

Chiral recognition of alpha-hydroxy acids has been achieved, and mixtures of enantiomers have been quantified in the gas phase, by using the kinetics of competitive unimolecular dissociation of singly-charged transition metal ion-bound trimeric complexes, [M(II)(A)(ref*)(2)-H](+) (M(II)=divalent transition metal ion; A=alpha-hydroxy acid; ref*=chiral reference ligand), to form the dimeric complexes [M(II)(A)(ref*)-H](+) and [M(II)(ref*)(2)-H](+). Chiral selectivity, the ratio of these two fragment ion abundances for the complex containing the analyte in one enantiomeric form expressed relative to that for the fragments of the corresponding complex containing the other enantiomer, ranges from 0.65 to 7.32. Chiral differentiation is highly dependent on the choice of chiral reference compound and central metal ion. The different coordination geometry of complexes resulting from the different d-orbital electronic configurations of these transition metal ions plays a role in chiral discrimination. Of all the transition metal ions examined chiral recognition is lowest for Cu(II), because of large distortion of the coordination complexes, and hence weak metal-ligand interactions and small stereochemical effects. It seems that two independent pi-cation interactions occur when N-acetyl-substituted aromatic amino acids used as the reference ligands and this accounts for improved chiral discrimination. If both metal-ligand and ligand-ligand interactions are optimized, large chiral selectivity is achieved. The sensitive nature of the methodology and the linear relationship between the logarithm of the fragment ion abundance ratio and the optical purity, which are intrinsic to the kinetic method, enable mixtures to be analyzed for small enantiomeric excess ( ee) by simply recording the ratios of fragment ion abundances in a tandem mass spectrum.

Calibration↗