Provided herein are several methods for selecting agents that bind to transmembrane receptors in a conformationally-selective way. In some embodiments, the method may comprise producing: a transmembrane receptor in an active conformation; and said transmembrane receptor in an inactive conformation and using cell sorting to select, from a population of cells comprising a library of cell surface-tethered extracellular capture agents, cells that are specifically bound to either the transmembrane receptor in its active conformation or the transmembrane receptor in its inactive conformation, but not both. In other embodiments, the method may comprise: contacting a GPCR with a population of cells that comprise a library of surface-tethered extracellular proteins; labeling the cell population with a conformationally-specific binding agent, e.g., a G-protein or mimetic thereof; and using cell sorting to select from the cell population cells that bind to the agent.

Provided herein are methods for labeling the proteomes of cells, as well as methods for labeling proteins or populations of proteins produced by cells. In some embodiments, the methods comprise introducing variant aminoacyl-tRNA synthetases and noncanonical amino acids into cells. Also provided herein are polynucleotides encoding variant aminoacyl-tRNA synthetases that recognize noncanonical amino acids. The methods and compositions provided herein are useful for, among other things, identifying target cells and identifying biomarkers of interest.

The invention discloses a detergent-compatible protein assay method, composition and kit based on bio-conjugation reaction between protein and Meldrum's acid activated furfural. The method includes adding MAF in dimethyl sulfoxide (DMSO) to a protein sample solution. The amine functionalities present on the amino acid residues reacts with the MAF instantaneously at room temperature to yield deep purple colored solutions of the corresponding conjugated proteins. The reagent composition added to protein may be in the range of 90-450 mM. The intensities of purple colored solutions were proportional to the protein concentration captured by spectrophotometric measurements. The assay is sensitive in the range of 0.125-15 mg/mL, is compatible with commonly used detergents and reducing agents in protein solutions and may be employed for estimation of protein samples in the presence of detergents and reducing agents.

Systems and methods for automated sample preparation and processing of protein corona are described herein, as well as its application in the discovery of advanced diagnostic tools as well as therapeutic agents.

The present invention relates to methods and products associated with in vivo enzyme profiling. In particular, the invention relates to methods of in vivo processing of exogenous molecules followed by detection of signature molecules as representative of the presence of active enzymes associated with diseases or conditions. The invention also relates to products, kits, and databases for use in the methods of the invention.

The presently disclosed subject matter provides methods using mass spectrometry for direct profiling of N-linked glycans from a biological sample. In addition, the embodiments of the present invention also disclose novel methods, known as targeted analyte detection (TAD), for improving the detection limit of MALDI-MS. These methods take advantage of the carrier effect of the added standard analytes, which occurs due to the generic sigmoidal shape of the calibration curve. The functionality of TAD depends on the relative enhancement of sensitivity over the increase of the standard deviation at the analysis of target analytes with spiking in exogenous concentration. At certain ranges of exogenous concentration, the increment in the sensitivity overcomes the standard deviation, resulting in an improved LOD. Theoretically, exogenous concentrations approximately at 1 LODorig would generate the optimum LOD improvement. TAD is a cost-effective LOD improvement method, which is not limited to a certain group of analytes, or detection methods or instruments. It can be applied to enhance the detection of any analyte with different detection methods, provided that the analyte of interest can be extracted or is available in synthetic form.

The present invention provides a method of preparing a sample comprising one or more proteins of interest, the method comprising: providing a sample comprising a population of proteins of interest solubilised with a surfactant in a medium; exposing said sample to a mild precipitant to cause precipitation of said proteins; during or after the precipitation step, bringing said sample into contact with a matrix adapted to capture said precipitated proteins and prevent excessive aggregation of precipitated protein particles; and washing the matrix with captured precipitated proteins to remove the surfactant. A sample preparation device to carry out the same is also provided.

The present invention provides compositions comprising chimeric polypeptides that bind to free ubiquitin proteins or free ubiquitin-like proteins with high affinity, as well as chimeric polypeptides that bind to both free and conjugated ubiquitin proteins or free and conjugated ubiquitin-like proteins, and methods of using the chimeric polypeptides to determine the amount of free or total ubiquitin or free or total ubiquitin-like proteins in various types of samples.

The present invention provides compositions and methods that can be used to determine a peptide signature for an antibody repertoire in a sample comprising multiple antibodies. The method can be used to characterize a phenotype in a sample, such as providing a diagnosis, prognosis or theranosis of a medical condition.

A method for determining in a sample, by mass spectrometry, the amount of one or more analytes selected from the group consisting of 12,13-DiHOME, 3-hydroxybutyrate (BHBA), 3-hydroxyoctanoate, 3-methylglutarylcarnitine, 3-ureidopropionate, 7-alpha-hydroxy-4-cholesten-3-one (7-Hoca), citrate, fucose, fumarate, gamma-tocopherol, glutamate, glutarate, glycerol, glycochenodeoxycholate, glycocholate, hypoxanthine, maleate, malonate, mannose, orotate, 2,3-pyrdinedicarboxylate, ribose, serine, taurine, taurochenodeoxycholate, taurocholate, palmitoleate, linolenate, xanthine, xylitol, and combinations thereof is described. The method comprises subjecting the sample to an ionization source under conditions suitable to produce one or more ions detectable by mass spectrometry from each of the one or more analytes; measuring, by mass spectrometry, the amount of the one or more ions from each of the one or more analytes; and using the measured amount to determine the amount of each of the one or more analytes in the sample.