Search tips
Search criteria

Results 1-4 (4)

Clipboard (0)

Select a Filter Below

Year of Publication
Document Types
1.  Quantitative Phosphoproteomics Unravels Biased Phosphorylation of Serotonin 2A Receptor at Ser280 by Hallucinogenic versus Nonhallucinogenic Agonists* 
The serotonin 5-HT2A receptor is a primary target of psychedelic hallucinogens such as lysergic acid diethylamine, mescaline, and psilocybin, which reproduce some of the core symptoms of schizophrenia. An incompletely resolved paradox is that only some 5-HT2A receptor agonists exhibit hallucinogenic activity, whereas structurally related agonists with comparable affinity and activity lack such a psychoactive activity. Using a strategy combining stable isotope labeling by amino acids in cell culture with enrichment in phosphorylated peptides by means of hydrophilic interaction liquid chromatography followed by immobilized metal affinity chromatography, we compared the phosphoproteome in HEK-293 cells transiently expressing the 5-HT2A receptor and exposed to either vehicle or the synthetic hallucinogen 1-[2,5-dimethoxy-4-iodophenyl]-2-aminopropane (DOI) or the nonhallucinogenic 5-HT2A agonist lisuride. Among the 5995 identified phosphorylated peptides, 16 sites were differentially phosphorylated upon exposure of cells to DOI versus lisuride. These include a serine (Ser280) located in the third intracellular loop of the 5-HT2A receptor, a region important for its desensitization. The specific phosphorylation of Ser280 by hallucinogens was further validated by quantitative mass spectrometry analysis of immunopurified receptor digests and by Western blotting using a phosphosite specific antibody. The administration of DOI, but not of lisuride, to mice, enhanced the phosphorylation of 5-HT2A receptors at Ser280 in the prefrontal cortex. Moreover, hallucinogens induced a less pronounced desensitization of receptor-operated signaling in HEK-293 cells and neurons than did nonhallucinogenic agonists. The mutation of Ser280 to aspartic acid (to mimic phosphorylation) reduced receptor desensitization by nonhallucinogenic agonists, whereas its mutation to alanine increased the ability of hallucinogens to desensitize the receptor. This study reveals a biased phosphorylation of the 5-HT2A receptor in response to hallucinogenic versus nonhallucinogenic agonists, which underlies their distinct capacity to desensitize the receptor.
PMCID: PMC4014284  PMID: 24637012
2.  Prophossi: automating expert validation of phosphopeptide–spectrum matches from tandem mass spectrometry 
Bioinformatics  2010;26(17):2153-2159.
Motivation: Complex patterns of protein phosphorylation mediate many cellular processes. Tandem mass spectrometry (MS/MS) is a powerful tool for identifying these post-translational modifications. In high-throughput experiments, mass spectrometry database search engines, such as MASCOT provide a ranked list of peptide identifications based on hundreds of thousands of MS/MS spectra obtained in a mass spectrometry experiment. These search results are not in themselves sufficient for confident assignment of phosphorylation sites as identification of characteristic mass differences requires time-consuming manual assessment of the spectra by an experienced analyst. The time required for manual assessment has previously rendered high-throughput confident assignment of phosphorylation sites challenging.
Results: We have developed a knowledge base of criteria, which replicate expert assessment, allowing more than half of cases to be automatically validated and site assignments verified with a high degree of confidence. This was assessed by comparing automated spectral interpretation with careful manual examination of the assignments for 501 peptides above the 1% false discovery rate (FDR) threshold corresponding to 259 putative phosphorylation sites in 74 proteins of the Trypanosoma brucei proteome. Despite this stringent approach, we are able to validate 80 of the 91 phosphorylation sites (88%) positively identified by manual examination of the spectra used for the MASCOT searches with a FDR < 15%.
Conclusions:High-throughput computational analysis can provide a viable second stage validation of primary mass spectrometry database search results. Such validation gives rapid access to a systems level overview of protein phosphorylation in the experiment under investigation.
Availability: A GPL licensed software implementation in Perl for analysis and spectrum annotation is available in the supplementary material and a web server can be assessed online at
Supplementary information: Supplementary data are available at Bioinformatics online.
PMCID: PMC2922888  PMID: 20651112
3.  Differential 14-3-3 Affinity Capture Reveals New Downstream Targets of Phosphatidylinositol 3-Kinase Signaling* 
We devised a strategy of 14-3-3 affinity capture and release, isotope differential (d0/d4) dimethyl labeling of tryptic digests, and phosphopeptide characterization to identify novel targets of insulin/IGF1/phosphatidylinositol 3-kinase signaling. Notably four known insulin-regulated proteins (PFK-2, PRAS40, AS160, and MYO1C) had high d0/d4 values meaning that they were more highly represented among 14-3-3-binding proteins from insulin-stimulated than unstimulated cells. Among novel candidates, insulin receptor substrate 2, the proapoptotic CCDC6, E3 ubiquitin ligase ZNRF2, and signaling adapter SASH1 were confirmed to bind to 14-3-3s in response to IGF1/phosphatidylinositol 3-kinase signaling. Insulin receptor substrate 2, ZNRF2, and SASH1 were also regulated by phorbol ester via p90RSK, whereas CCDC6 and PRAS40 were not. In contrast, the actin-associated protein vasodilator-stimulated phosphoprotein and lipolysis-stimulated lipoprotein receptor, which had low d0/d4 scores, bound 14-3-3s irrespective of IGF1 and phorbol ester. Phosphorylated Ser19 of ZNRF2 (RTRAYpS19GS), phospho-Ser90 of SASH1 (RKRRVpS90QD), and phospho- Ser493 of lipolysis-stimulated lipoprotein receptor (RPRARpS493LD) provide one of the 14-3-3-binding sites on each of these proteins. Differential 14-3-3 capture provides a powerful approach to defining downstream regulatory mechanisms for specific signaling pathways.
PMCID: PMC2773716  PMID: 19648646
4.  Identifying specific protein interaction partners using quantitative mass spectrometry and bead proteomes 
The Journal of Cell Biology  2008;183(2):223-239.
The identification of interaction partners in protein complexes is a major goal in cell biology. Here we present a reliable affinity purification strategy to identify specific interactors that combines quantitative SILAC-based mass spectrometry with characterization of common contaminants binding to affinity matrices (bead proteomes). This strategy can be applied to affinity purification of either tagged fusion protein complexes or endogenous protein complexes, illustrated here using the well-characterized SMN complex as a model. GFP is used as the tag of choice because it shows minimal nonspecific binding to mammalian cell proteins, can be quantitatively depleted from cell extracts, and allows the integration of biochemical protein interaction data with in vivo measurements using fluorescence microscopy. Proteins binding nonspecifically to the most commonly used affinity matrices were determined using quantitative mass spectrometry, revealing important differences that affect experimental design. These data provide a specificity filter to distinguish specific protein binding partners in both quantitative and nonquantitative pull-down and immunoprecipitation experiments.
PMCID: PMC2568020  PMID: 18936248

Results 1-4 (4)