Chunxia Zou

Boston University, Boston, Massachusetts, United States

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Publications (3)15.37 Total impact

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    ABSTRACT: One of the principal goals of glycoprotein research is to correlate glycan structure and function. Such correlation is necessary to understand the mechanisms whereby glycoprotein structure elaborates the functions of myriad proteins. Accurate comparison of glycoforms and quantification of glycosites is an essential step in this direction. Mass spectrometry has emerged as a powerful analytical technique in the field of glycoprotein characterization. Its sensitivity, high dynamic range, and mass accuracy provide both quantitative and sequence/structural information. As part of the 2012 ABRF Glycoprotein Research Group (gPRG) study, we explored the use of mass spectrometry and ancillary methodologies to characterize the glycoforms of two sources of human prostate specific antigen (PSA). PSA is used as a tumor marker for prostate cancer, with increasing blood levels used to distinguish between normal and cancer states. The glycans on PSA are believed to be biantennary N-linked and it has been observed that prostate cancer tissues and cell lines, contain more antennae than the benign form. Thus, the ability to quantify differences in glycosylation associated with cancer has the potential to positively impact use of PSA as a biomarker. We studied standard peptide based proteomics/glycomics methodologies including LC-MS/MS for peptide/glycopeptide sequencing and label-free approaches for differential quantification. We performed an interlaboratory study to determine the ability of different laboratories to correctly characterize the differences in glycoforms between two different sources using mass spectrometry methods. We used clustering analysis and ancillary statistical data treatment on the data sets submitted by participating laboratories to obtain a consensus of the glycoforms and abundances. The results demonstrate the relative strengths and weaknesses of top-down glycoproteomics, bottom-up glycoproteomics, and glycomics methods, respectively.
    Molecular &amp Cellular Proteomics 06/2013; · 7.25 Impact Factor
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    ABSTRACT: The glycan of specific proteins can dictate the response of cells to stimuli, and thus their phenotype. We describe a chemical strategy to modify the cellular glycoform of T cells, which resulted in a modified cellular response. Our data indicate that chemical modification of the phosphatase CD45 is responsible for the observed differences in response to receptor cross-linking. By increasing the content of galactose epitopes in the glycocalyx of a lymphoma cell line, we were able to increase the response of the cell to lectin stimulation through the glycoprotein receptor, CD45. The method described here exploits metabolic labeling of a cell to reprogram the cellular response to external stimuli though changes in the number of lectin binding sites on the cell surface.
    Bioconjugate Chemistry 06/2013; · 4.58 Impact Factor
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    ABSTRACT: The mammalian neuraminidase (NEU) enzymes are found in diverse cellular compartments. Members of the family, such as NEU2 and NEU1, are cytosolic or lysosomal, while NEU3 and NEU4 are membrane-associated. NEU enzymes that act on substrates in the plasma membrane could modulate cellular signaling, cell surface glycoforms and the composition of plasma membrane glycolipids. Therefore, their substrates and mechanism of action are of interest for discerning their physiological roles. We have studied the structure of the human NEU3 using molecular modeling to predict residues involved in the recognition and hydrolysis of glycolipid substrates. To test the model, we have used site-directed mutagenesis of the recombinant protein. Enzymatic studies of the relative activity of these mutants, as well as their pH profiles and inhibition by 2-deoxy-2,3-dehydro-N-acetylneuraminic acid, are reported. Using nuclear magnetic resonance spectroscopy, we confirmed that the enzyme is a retaining exo-sialidase, and we propose that the key catalytic residues of the enzyme consist of the general acid-base D50 and the nucleophilic Y370-E225 pair. Mutations of residues expected to interact directly with the sialic acid N5-acetyl (A160, M87, I105) and C7-C9 glycerol side-chain (E113, Y179, Y181) reduced enzymatic activity. We identified several active mutants of the enzyme which contain modifications at the periphery of the active site. Truncations at the N- or C-terminus of more than 10 residues abolished enzyme activity. We propose a catalytic mechanism consistent with the data and identify residues that contribute to glycolipid recognition.
    Glycobiology 09/2010; 20(9):1127-38. · 3.54 Impact Factor