Various stable isotope labeling (SIL) techniques have recently emerged to improve the efficiency and accuracy of protein quantitation by mass spectrometry (MS). We have developed a mass-tagging strategy to incorporate stable isotope tagged amino acids into cellular proteins in a residue-specific manner during cell growth. In this study, we further extend this residue-specific SIL approach to the accurate quantitation of protein abundances in different cell populations. For proteins whose expression levels are the same in cells grown in the normal and labeled media, the relative areas of the normal (light) and labeled (heavy) isotopic peaks are linearly correlated with the cells mixing ratios. This approach was first used to determine the effect of the zinc-responsive transcription factor Zap1 on the yeast proteome. Ten protein spots from a PAGE gel were chosen randomly and their differential protein expression levels in wild-type and zap1delta cells were readily determined by the isotopic ratio. Methionine synthase (Met6) was identified to be up-regulated more than four times in the zap1delta mutant strain whereas the expression level of other nine proteins remained unchanged. Further, we applied this strategy to study the cellular response to radiation in human skin fibroblast cells. Analyzing one protein band randomly selected from SDS-PAGE, the expression level of a novel protein was found to increase two-fold in response to radiation whereas the expression level of a control protein remained unchanged. This strategy is generally applicable using any particular type of amino acid as the labeling precursors for accurate quantitation of protein relative abundances.

Mycobacterium tuberculosis is an infectious microorganism that causes human tuberculosis. The cell membranes of pathogens are known to be rich in possible diagnostic and therapeutic protein targets. To compliment the M. tuberculosis genome, we have profiled the membrane protein fraction of the M. tuberculosis H37Rv strain using an analytical platform that couples one-dimensional SDS gels to a microcapillary liquid chromatography-nanospray-tandem mass spectrometer. As a result, 739 proteins have been identified by two or more distinct peptide sequences and have been characterized. Interestingly, ϳ ϳ450 proteins represent novel identifications, 79 of which are membrane proteins and more than 100 of which are membrane-associated proteins. The physicochemical properties of the identified proteins were studied in detail, and then biological functions were obtained by sorting them according to Sanger Institute gene function category. Many membrane proteins were found to be involved in the cell envelope, and those proteins with energy metabolic functions were also identified in this study. Molecular & Cellular Proteomics 2:1284 -1296, 2003.Tuberculosis (TB) 1 is the major cause of death from an infectious disease in the world resulting in an estimated 8.5 million cases of clinical tuberculosis and 3 million deaths/year (1). The emergence of TB associated with HIV and multidrugresistant TB has increased the threat to public health. The World Health Organization recognized the global emergency of TB in 1993. Mycobacterium tuberculosis (MTB), the etiologic agent of TB, can replicate in host cells by escaping host cell defenses. The interactions between MTB and its host appear to be very delicately balanced (2, 3). Meanwhile, newly emerging drug-resistant strains of MTB are more difficult to cure, and they cause more fatal cases. Therefore, there are critical needs to identify new drugs or vaccines for MTB therapeutics. The recent completion of the genome sequence of the virulence MTB strain H37Rv (4) has provided new biomolecular insights into the mycobacterial cells.Proteomics, the global analysis of the proteins expressed in a cell or tissue, provides a very promising approach for the large scale identification of proteins, their complexes, and their functions (5), which is required for the design of more effective and precise therapeutics or drug design (6). Therefore, the proteomic analysis of MTB strains is critical for an understanding of the molecular basis of its virulence and pathogenicity. A number of proteomic studies, mainly twodimensional gel electrophoresis (2-DE)-based, have been carried out to identify proteins in various MTB strains and their subcellular localizations, including culture filtrate proteins and cell wall and cytosol fractions (7-12). These results demonstrate how the proteomics approaches complement genomics by profiling the protein products of the expressed genes. Further, the open reading frames in the MTB H37Rv strain that were not predicted from genomics were found by proteomics (13).In ...

No abstract

By using DNA nuclease digestion and a quantitative "dual tagging" proteomic approach that integrated mass spectrometry, stable isotope labeling, and affinity purification, we studied the histone H2AX-associating protein complex in chromatin in mammalian cells in response to ionizing radiation (IR). In the non-irradiated control cells, calmodulin (CaM) and the transcription elongation factor facilitates chromatin transcription (FACT) were associated with H2AX. Thirty minutes after exposing cells to IR the CaM and FACT complexes dissociated, whereas two DNA repair proteins, poly(ADP-ribose) polymerase-1 and DEAH box polypeptide 30 isoform 1, interacted with H2AX. Two hours and 30 min after exposure, none of the above proteins were in the complex. H2B, nucleophosmin/B23, and calreticulin were associated with H2AX in both non-irradiated and irradiated cells. The results suggest that the H2AX complex undergoes dynamic changes upon induction of DNA damage and during DNA repair. The genuine interactions between H2AX and H2B, nucleophosmin/B23, calreticulin, poly(ADP-ribose) polymerase-1, and CaM under each condition were validated by immunoprecipitation/Western blotting and mammalian two-hybrid assays. Because multiple Ca 2؉ -binding proteins were found in the H2AX complex, the roles of Ca 2؉ were examined. The results indicate that Ca 2؉ /CaM plays important roles in regulating IR-induced cell cycle arrest, possibly through mediating chromatin structure. The dataset presented here demonstrates that sensitive profiling of the dynamics of functional cellular protein-protein interactions can successfully lead to the dissection of important metabolic or signaling pathways.

All-trans-retinoic acid (ATRA) induces growth inhibition, differentiation, and apoptosis in cancer cells, including acute promyelocytic leukemia (APL). In APL, expression of promyelocytic leukemia protein retinoic acid receptor-␣ (PML-RAR␣) fusion protein, owing to the t(15; 17) reciprocal translocation, leads to a block in the promyelocytic stage of differentiation. Here, we studied molecular mechanisms involved in ATRA-induced growth inhibition and myeloid cell differentiation in APL. By employing comprehensive high-throughput proteomic methods of 2-dimensional (2-D) gel electrophoresis and amino acid-coded mass tagging coupled with electrospray ionization (ESI) mass spectrometry, we systematically identified a total of 59 differentially expressed proteins that were consistently modulated in response to ATRA treatment. The data revealed significant downregulation of eukaryotic initiation and elongation factors, initiation factor 2 (IF2), eukaryotic initiation factor 4AI (eIF4AI), eIF4G, eIF5, eIF6, eukaryotic elongation factor 1A-1 (eEF1A-1), EF-1-␦, eEF1␥, 14-3-3⑀, and 14-3-3/␦ (P < .05). The translational inhibitor DAP5/p97/NAT1 (deathassociated protein 5) and PML isoform-1 were found to be up-regulated (P < .05). Additionally, the down-regulation of heterogeneous nuclear ribonucleoproteins (hnRNPs) C1/C2, UP2, K, and F; small nuclear RNPs (snRNPs) D3 and E; nucleoprotein tumor potentiating region (TPR); and protein phosphatase 2A (PP2A) were found (P < .05); these were found to function in pre-mRNA processing, splicing, and export events. Importantly, these pro-