Protein kinases are coded by more than 2,000 genes and thus constitute the largest single enzyme family in the human genome. Most cellular processes are in fact regulated by the reversible phosphorylation of proteins on serine, threonine, and tyrosine residues. At least 30% of all proteins are thought to contain covalently bound phosphate. Despite the importance and widespread occurrence of this modification, identification of sites of protein phosphorylation is still a challenge, even when performed on highly purified protein. Reported here is methodology that should make it possible to characterize most, if not all, phosphoproteins from a whole-cell lysate in a single experiment. Proteins are digested with trypsin and the resulting peptides are then converted to methyl esters, enriched for phosphopeptides by immobilized metal-affinity chromatography (IMAC), and analyzed by nanoflow HPLC/electrospray ionization mass spectrometry. More than 1,000 phosphopeptides were detected when the methodology was applied to the analysis of a whole-cell lysate from Saccharomyces cerevisiae. A total of 216 peptide sequences defining 383 sites of phosphorylation were determined. Of these, 60 were singly phosphorylated, 145 doubly phosphorylated, and 11 triply phosphorylated. Comparison with the literature revealed that 18 of these sites were previously identified, including the doubly phosphorylated motif pTXpY derived from the activation loop of two mitogen-activated protein (MAP) kinases. We note that the methodology can easily be extended to display and quantify differential expression of phosphoproteins in two different cell systems, and therefore demonstrates an approach for "phosphoprofiling" as a measure of cellular states.

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Disease-associated blood biomarkers exist in exceedingly low concentrations within complex mixtures of high-abundance proteins such as albumin. We have introduced an affinity bait molecule into N-isopropylacrylamide to produce a particle that will perform three independent functions within minutes, in one step, in solution: a) molecular size sieving b) affinity capture of all solution phase target molecules, and c) complete protection of harvested proteins from enzymatic degradation. The captured analytes can be readily electroeluted for analysis.There is an urgent need to discover novel biomarkers that provide sensitive and specific disease detection1 , 2. Cancer is rapidly becoming the leading cause of death for many population groups in the United States, largely due to the fact that the disease is usually diagnosed after the cancer has metastasized and treatment is ineffective. It is widely believed that early detection of cancer prior to metastasis will lead to a dramatic improvement in treatment outcome. Biomarkers are nucleic acids, proteins, protein fragments or metabolites indicative of a specific biological state, that are associated with the risk of contraction or presence of disease3. Biomarker research has revealed that low-abundance circulating proteins and peptides present a rich source of information regarding the state of the organism as a whole 4 . Two major hurdles have prevented these discoveries from reaching clinical benefit: 1) disease-relevant biomarkers in blood or body fluids may exist in exceedingly low concentrations within a complex mixture of biomolecules and could be masked by high-abundance species such as albumin, and 2) degradation of protein biomarkers can occur immediately following the collection of blood or body fluid as a result of endogenous or exogenous proteinases. The goal of this study was to create "smart" nano-particles that allow enrichment and encapsulation of selected classes of proteins and peptides from complex mixtures of biomolecules such as plasma, and protect them from degradation during subsequent sample handling. The captured analytes can be readily extracted from the particles by electrophoresis allowing for subsequent quantitative analysis. This nanotechnology provides a powerful tool that is uniquely suited for the discovery of novel biomarkers for early stage diseases such as cancer.SUPPORTING INFORMATION AVAILABLE: Available in the Supplementary Information are details on particles synthesis protocol, SDS PAGE analysis on molecular sieving properties and enzymatic degradation, and tables (Table S1 and S2) listing proteins (with peptide coverage lists) identified via LC-MS/MS (ESI) on material electroeluted from NIPAm and NIPAm/AAc particles. This material is available free of charge via the Internet at http://pubs.acs.org. NIH Public AccessAuthor Manuscript Nano Lett. Author manuscript; available in PMC 2010 May 28. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author ManuscriptThe concentration of proteins and peptides comprising t...

CE-MS is a successful proteomic platform for the definition of biomarkers in different body fluids. Besides the biomarker defining experimental parameters, CE migration time and molecular weight, especially biomarker's sequence identity is an indispensable cornerstone for deeper insights into the pathophysiological pathways of diseases or for made-to-measure therapeutic drug design. Therefore, this report presents a detailed discussion of different peptide sequencing platforms consisting of high performance separation method either coupled on-line or off-line to different MS/MS devices, such as MALDI-TOF-TOF, ESI-IT, ESI-QTOF and Fourier transform ion cyclotron resonance, for sequencing indicative peptides. This comparison demonstrates the unique feature of CE-MS technology to serve as a reliable basis for the assignment of peptide sequence data obtained using different separation MS/MS methods to the biomarker defining parameters, CE migration time and molecular weight. Discovery of potential biomarkers by CE-MS enables sequence analysis via MS/MS with platform-independent sample separation. This is due to the fact that the number of basic and neutral polar amino acids of biomarkers sequences distinctly correlates with their CE-MS migration time/molecular weight coordinates. This uniqueness facilitates the independent entry of different sequencing platforms for peptide sequencing of CE-MS-defined biomarkers from highly complex mixtures.

We describe the use of capillary electrophoresis (CE) coupled with mass spectrometry (MS) to identify single polypeptides and patterns of polypeptides specific for prostate cancer (CaP) in human urine. Using improved sample preparation methods that enable enhanced comparability between different samples, we examined samples from 47 patients who underwent prostate biopsy. Of this group, 21 patients had benign pathology and 26 with CaP, and these were used to define potential biomarkers, which allow discrimination between these two states. In addition, CE-MS data from these 47 urine samples were compared to that of 41 young men (control) without known or suspected clinical CaP to further confirm the polypeptides indicative for CaP. Upon crossvalidation of the same samples, several polypeptides were selected that enabled correct classification of the CaP patients with 92% sensitivity and 96% specificity. We then examined an additional 474 samples from patients with renal disease enrolled in other studies and found that 14 (3%) had polypeptides suggestive of CaP possibly indicating that they harbor clinical CaP. In conclusion, this early pilot study suggests that CE-MS of urine warrants further investigation as a tool that can identify putative biomarkers for CaP.