Nonisotopic reagents for a cost-effective increase in sample throughput of targeted quantitative proteomics.

The new technology of ultrathroughput MS (uMS) transforms the intrinsic capability of analyte multiplexing in mass spectrometry (MS) to sample multiplexing. Core technological advantages of uMS rely on the decoupled use of isotopic quantitation reference and nonisotopic mass coding of samples. These advantages include: (1) high sample-throughput potential, (2) utilization of minimal amounts of expensive stable isotopes for the quantitation reference, and (3) unleashing of the open-source exploration of the chemical structure diversity of nonisotopic reagents to significantly enhance the MS detectability of analytes. A particular uMS method, ultrathroughput multiple reaction monitoring (uMRM), is reported for one-experiment quantitation of a surrogate peptide (SVILLGR) of prostate specific antigen (PSA) in multiple serum samples. Following derivatization of the pair of spiked, isotopic reference (SVILLGR*) and endogenous, native peptide in each sample, all samples were pooled for a step of simultaneous enrichment and cleanup of derivatized peptide pairs using immobilized antibody. The MS analysis of the pooled sample reported the quantity and sample origin of the surrogate peptide. Several analyses with different sample throughput were presented, with the highest being 15-in-1. Screening of nonisotopic reagents used combinatorial libraries of peptidyl compounds, and the reagent selection was based on the derivatization effectiveness and the capability of MS signal enhancement for the peptide. The precision, accuracy, and linearity of the uMRM MS technology were found to be comparable with standard isotope dilution MRM MS.

Improvement of a synthetic live bacterial therapeutic for phenylketonuria with biosensor-enabled enzyme engineering.

In phenylketonuria (PKU) patients, a genetic defect in the enzyme phenylalanine hydroxylase (PAH) leads to elevated systemic phenylalanine (Phe), which can result in severe neurological impairment. As a treatment for PKU, Escherichia coli Nissle (EcN) strain SYNB1618 was developed under Synlogic's Synthetic Biotic™ platform to degrade Phe from within the gastrointestinal (GI) tract. This clinical-stage engineered strain expresses the Phe-metabolizing enzyme phenylalanine ammonia lyase (PAL), catalyzing the deamination of Phe to the non-toxic product trans-cinnamate (TCA). In the present work, we generate a more potent EcN-based PKU strain through optimization of whole cell PAL activity, using biosensor-based high-throughput screening of mutant PAL libraries. A lead enzyme candidate from this screen is used in the construction of SYNB1934, a chromosomally integrated strain containing the additional Phe-metabolizing and biosafety features found in SYNB1618. Head-to-head, SYNB1934 demonstrates an approximate two-fold increase in in vivo PAL activity compared to SYNB1618.

Development of a synthetic live bacterial therapeutic for the human metabolic disease phenylketonuria.

Phenylketonuria (PKU) is a genetic disease that is characterized by an inability to metabolize phenylalanine (Phe), which can result in neurotoxicity. To provide a potential alternative to a protein-restricted diet, we engineered Escherichia coli Nissle to express genes encoding Phe-metabolizing enzymes in response to anoxic conditions in the mammalian gut. Administration of our synthetic strain, SYNB1618, to the Pahenu2/enu2 PKU mouse model reduced blood Phe concentration by 38% compared with the control, independent of dietary protein intake. In healthy Cynomolgus monkeys, we found that SYNB1618 inhibited increases in serum Phe after an oral Phe dietary challenge. In mice and primates, Phe was converted to trans-cinnamate by SYNB1618, quantitatively metabolized by the host to hippurate and excreted in the urine, acting as a predictive biomarker for strain activity. SYNB1618 was detectable in murine or primate feces after a single oral dose, permitting the evaluation of pharmacodynamic properties. Our results define a strategy for translation of live bacterial therapeutics to treat metabolic disorders.

Peptide dimethylation: fragmentation control via distancing the dimethylamino group.

Direct reductive methylation of peptides is a common method for quantitative proteomics. It is an active derivatization technique; with participation of the dimethylamino group, the derivatized peptides preferentially release intense a1 ions. The advantageous generation of a1 ions for quantitative proteomic profiling, however, is not desirable for targeted proteomic quantitation using multiple reaction monitoring mass spectrometry; this mass spectrometric method prefers the derivatizing group to stay with the intact peptide ions and multiple fragments as passive mass tags. This work investigated collisional fragmentation of peptides whose amine groups were derivatized with five linear ω-dimethylamino acids, from 2-(dimethylamino)-acetic acid to 6-(dimethylamino)-hexanoic acid. Tandem mass spectra of the derivatized tryptic peptides revealed different preferential breakdown pathways. Together with energy resolved mass spectrometry, it was found that shutting down the active participation of the terminal dimethylamino group in fragmentation of derivatized peptides is possible. However, it took a separation of five methylene groups between the terminal dimethylamino group and the amide formed upon peptide derivatization. For the first time, the gas-phase fragmentation of peptides derivatized with linear ω-dimethylamino acids of systematically increasing alkyl chain lengths is reported.

Quantitative protein analysis using enzymatic [¹8O]water labeling.

This unit describes the stepwise procedure for differential oxygen isotope labeling of peptides and mass spectrometric quantification of relative protein levels in comparative proteomic experiments. The [¹8O] labeling of peptides happens at the peptide C-terminus and is achieved via the enzymatic oxygen exchange of tryptic peptides via catalysis of immobilized trypsin. Experimental considerations in effective incorporation and stabilization of the oxygen labels are discussed. Methods for mass spectrometric quantification of peptides with differential [¹6O] and [¹8O] isotopes are presented.