Noncanonical Amino Acid Tagging Research Articles

Quantitative, Time-Resolved Proteomic Analysis by Combining Bioorthogonal Noncanonical Amino Acid Tagging and Pulsed Stable Isotope Labeling by Amino Acids in Cell Culture

An approach to proteomic analysis that combines bioorthogonal noncanonical amino acid tagging (BONCAT) and pulsed stable isotope labeling with amino acids in cell culture (pSILAC) provides accurate quantitative information about rates of cellular protein synthesis on time scales of minutes. The method is capable of quantifying 1400 proteins produced by HeLa cells during a 30 min interval, a time scale that is inaccessible to isotope labeling techniques alone. Potential artifacts in protein quantification can be reduced to insignificant levels by limiting the extent of noncanonical amino acid tagging. We find no evidence for artifacts in protein identification in experiments that combine the BONCAT and pSILAC methods.

In situ visualization of newly synthesized proteins in environmental microbes using amino acid tagging and click chemistry

Here we describe the application of a new click chemistry method for fluorescent tracking of protein synthesis in individual microorganisms within environmental samples. This technique, termed bioorthogonal non-canonical amino acid tagging (BONCAT), is based on the in vivo incorporation of the non-canonical amino acid L-azidohomoalanine (AHA), a surrogate for l-methionine, followed by fluorescent labelling of AHA-containing cellular proteins by azide-alkyne click chemistry. BONCAT was evaluated with a range of phylogenetically and physiologically diverse archaeal and bacterial pure cultures and enrichments, and used to visualize translationally active cells within complex environmental samples including an oral biofilm, freshwater and anoxic sediment. We also developed combined assays that couple BONCAT with ribosomal RNA (rRNA)-targeted fluorescence in situ hybridization (FISH), enabling a direct link between taxonomic identity and translational activity. Using a methanotrophic enrichment culture incubated under different conditions, we demonstrate the potential of BONCAT-FISH to study microbial physiology in situ. A direct comparison of anabolic activity using BONCAT and stable isotope labelling by nano-scale secondary ion mass spectrometry (15NH3 assimilation) for individual cells within a sediment-sourced enrichment culture showed concordance between AHA-positive cells and 15N enrichment. BONCAT-FISH offers a fast, inexpensive and straightforward fluorescence microscopy method for studying the in situ activity of environmental microbes on a single-cell level.

Acute Synthesis of CPEB Is Required for Plasticity of Visual Avoidance Behavior in Xenopus

Neural plasticity requires protein synthesis, but theidentity of newly synthesized proteins generated in response to plasticity-inducing stimuli remains unclear. We used invivo bio-orthogonal noncanonical amino acid tagging (BONCAT) with the methionine analog azidohomoalanine (AHA) combined with themultidimensional protein identification technique (MudPIT) to identify proteins that are synthesized inthe tadpole brain over 24hr. We induced conditioning-dependent plasticity of visual avoidance behavior, which required N-methyl-D-aspartate (NMDA) and Ca(2+)-permeable α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors, αCaMKII, and rapid protein synthesis. Combining BONCAT with western blots revealed that proteins including αCaMKII, MEK1, CPEB, and GAD65 are synthesized during conditioning. Acute synthesis of CPEB during conditioning is required for behavioral plasticity as well asconditioning-induced synaptic and structural plasticity in the tectal circuit. We outline a signaling pathway that regulates protein-synthesis-dependent behavioral plasticity in intact animals, identify newly synthesized proteins induced by visual experience, and demonstrate a requirement for acute synthesis of CPEB in plasticity.

Identification of secreted bacterial proteins by noncanonical amino acid tagging

Pathogenic microbes have evolved complex secretion systems to deliver virulence factors into host cells. Identification of these factors is critical for understanding the infection process. We report a powerful and versatile approach to the selective labeling and identification of secreted pathogen proteins. Selective labeling of microbial proteins is accomplished via translational incorporation of azidonorleucine (Anl), a methionine surrogate that requires a mutant form of the methionyl-tRNA synthetase for activation. Secreted pathogen proteins containing Anl can be tagged by azide-alkyne cycloaddition and enriched by affinity purification. Application of the method to analysis of the type III secretion system of the human pathogen Yersinia enterocolitica enabled efficient identification of secreted proteins, identification of distinct secretion profiles for intracellular and extracellular bacteria, and determination of the order of substrate injection into host cells. This approach should be widely useful for the identification of virulence factors in microbial pathogens and the development of potential new targets for antimicrobial therapy.

Metabolic Turnover of Synaptic Proteins: Kinetics, Interdependencies and Implications for Synaptic Maintenance

Chemical synapses contain multitudes of proteins, which in common with all proteins, have finite lifetimes and therefore need to be continuously replaced. Given the huge numbers of synaptic connections typical neurons form, the demand to maintain the protein contents of these connections might be expected to place considerable metabolic demands on each neuron. Moreover, synaptic proteostasis might differ according to distance from global protein synthesis sites, the availability of distributed protein synthesis facilities, trafficking rates and synaptic protein dynamics. To date, the turnover kinetics of synaptic proteins have not been studied or analyzed systematically, and thus metabolic demands or the aforementioned relationships remain largely unknown. In the current study we used dynamic Stable Isotope Labeling with Amino acids in Cell culture (SILAC), mass spectrometry (MS), Fluorescent Non–Canonical Amino acid Tagging (FUNCAT), quantitative immunohistochemistry and bioinformatics to systematically measure the metabolic half-lives of hundreds of synaptic proteins, examine how these depend on their pre/postsynaptic affiliation or their association with particular molecular complexes, and assess the metabolic load of synaptic proteostasis. We found that nearly all synaptic proteins identified here exhibited half-lifetimes in the range of 2–5 days. Unexpectedly, metabolic turnover rates were not significantly different for presynaptic and postsynaptic proteins, or for proteins for which mRNAs are consistently found in dendrites. Some functionally or structurally related proteins exhibited very similar turnover rates, indicating that their biogenesis and degradation might be coupled, a possibility further supported by bioinformatics-based analyses. The relatively low turnover rates measured here (∼0.7% of synaptic protein content per hour) are in good agreement with imaging-based studies of synaptic protein trafficking, yet indicate that the metabolic load synaptic protein turnover places on individual neurons is very substantial.

QuaNCAT: quantitating proteome dynamics in primary cells

Here we demonstrate that quantitation of stimuli-induced proteome dynamics in primary cells is feasible by combining the power of Bio-Orthogonal Non Canonical Amino acid Tagging (BONCAT) and Stable Isotope Labelling of Amino acids in Cell culture (SILAC). In conjunction with nanoLC-MS/MS QuaNCAT allowed us to monitor the early expression changes of > 600 proteins in primary resting T cells subjected to activation stimuli.

A Novel Role of Cytosolic Protein Synthesis Inhibition in Aminoglycoside Ototoxicity

Ototoxicity is a main dose-limiting factor in the clinical application of aminoglycoside antibiotics. Despite longstanding research efforts, our understanding of the mechanisms underlying aminoglycoside ototoxicity remains limited. Here we report the discovery of a novel stress pathway that contributes to aminoglycoside-induced hair cell degeneration. Modifying the previously developed bioorthogonal noncanonical amino acid tagging method, we used click chemistry to study the role of protein synthesis activity in aminoglycoside-induced hair cell stress. We demonstrate that aminoglycosides inhibit protein synthesis in hair cells and activate a signaling pathway similar to ribotoxic stress response, contributing to hair cell degeneration. The ability of a particular aminoglycoside to inhibit protein synthesis and to activate the c-Jun N-terminal kinase (JNK) pathway correlated well with its ototoxic potential. Finally, we report that a Food and Drug Administration-approved drug known to inhibit ribotoxic stress response also prevents JNK activation and improves hair cell survival, opening up novel strategies to prevent and treat aminoglycoside ototoxicity.

Focus on Brain Proteins and Proteomics

Focus on Brain Proteins and Proteomics

Defining TNF-α and IL-1β induced nascent proteins: Combining bio‐orthogonal non‐canonical amino acid tagging and proteomics

An impediment in the development of new therapeutic strategies for chronic inflammatory diseases is the limited understanding of underlying molecular mechanisms. The objective of this study was to identify newly synthesized (nascent) proteins induced by critical inflammatory cytokines TNF-α and IL-1β in human monocytic THP-1 cells. We optimized methods to combine two different approaches, bio‐orthogonal non-canonical amino acid tagging (BONCAT) along with proteomics using isobaric tags (iTRAQ). BONCAT employed the incorporation of l-azidohomoalanine (AHA), an analog of methionine, into TNF-α or IL-1β induced nascent proteins. The AHA-containing nascent proteins were tagged with alkyne-biotin to allow enrichment using avidin affinity purification. The differential expressions of the enriched proteins were further determined using iTRAQ reagents and mass spectrometry (MS). The combination of BONCAT and proteomics represents a unique approach that has uncovered the nascent proteome induced by inflammatory cytokines TNF-α and IL-1β.

Dynamic Monitoring of Newly Synthesized Proteomes: Up-Regulation of Myristoylated Protein Kinase A During Butyric Acid Induced Apoptosis

Post-translational modification (PTM) is a highly dynamic yet precisely controlled process by which most eukaryotic proteins are chemically diversified. Many critical cellular responses are mediated through PTMs, which lead to modulation of enzyme activity, protein conformation, protein–protein interaction, and cellular localization. Analysis of these modifications at the proteome level could provide invaluable biological insight but remains a technically challenging undertaking. Traditionally, PTMs have been studied by standard molecular biology techniques involving tedious isolation of individual proteins and subsequent direct detection and analysis of amino acids bearing the modification. Recent advances in mass spectrometry, when combined with stable-isotope or metabolic labeling approaches, have enabled several large-scale studies of PTMs and their dynamics. These methods, however, analyze PTM changes of all proteins (old and new) present in the cell at the time of sampling and thus are only able to evaluate PTM dynamics at the ensemble level. With unnatural metabolic building blocks and in vivo compatible conjugation chemistries becoming increasingly available (Scheme 1), we sought to develop a proteomic strategy for the detection and identification of newly synthesized proteomes and their PTMs (Figure 1). We envisioned several advantages of studying the PTM dynamics of newly synthesized proteomes: 1) this method decreases the complexity of the proteome and enables the identification of PTM changes that occur in a predefined protein synthesis window; 2) it gives an accurate estimate of the time scale of different PTM events in transforming newly synthesized, modification-free proteins into mature functional entities; 3) it permits PTM analysis of primary protein synthesis responses to internal and external cues. To isolate a newly synthesized proteome, wemade use of BONCAT (bio-orthogonal noncanonical amino acid tagging), which uses the known methionine surrogates azidohomoalanine (AHA) and homopropargylglycine (HPG) for metabolic incorporation into newly synthesized proteins (Scheme 1, blue) and the corresponding alkyneor azide-modified biotin reporter (Scheme 1, bottom) for subsequent proteome isolation. To monitor dynamic changes of an PTM event, we fed growing cells with an azideor alkynecontaining sugar, fatty acid, or lipid building block (Scheme 1, orange). It should be noted that while our work was in progress, Hang and co-workers reported a tandem labeling and detection method to monitor the dynamic acylation of LCK (a tyrosine kinase) and its turnover. Their work focused on the study of single PTM events (i.e. protein palmitoylation) of a specific protein (i.e., LCK) in a proteome. The work herein, while conceptually similar, greatly expands the scope of this double metabolic incorporation strategy by successfully demonstrating, for the first Scheme 1. Methionine surrogates (blue) and unnatural metabolite PTM probes (orange) form bio-orthogonal pairs for compatible double metabolic incorporation. Those forming pairs are boxed in the same group. Azideand alkyne-containing fluorophore and biotin reporters are also shown (bottom).

Identification and Quantitation of Newly Synthesized Proteins in Escherichia coli by Enrichment of Azidohomoalanine-labeled Peptides with Diagonal Chromatography

A method is presented to identify and quantify several hundreds of newly synthesized proteins in Escherichia coli upon pulse labeling cells with the methionine analogue azidohomoalanine (azhal). For the first 30 min after inoculation, a methionine-auxotrophic strain grows equally well on azhal as on methionine. Upon a pulse of 15 min and digestion of total protein, azhal-labeled peptides are isolated by a retention time shift between two reversed phase chromatographic runs. The retention time shift is induced by a reaction selective for the azido group in labeled peptides using tris(2-carboxyethyl)phosphine. Selectively modified peptides are identified by reversed phase liquid chromatography and on-line tandem mass spectrometry. We identified 527 proteins representative of all major Gene Ontology categories. Comparing the relative amounts of 344 proteins synthesized in 15 min upon a switch of growth temperature from 37 to 44 degrees C showed that nearly 20% increased or decreased more than 2-fold. Among the most up-regulated proteins many were chaperones and proteases in accordance with the cells response to unfolded proteins due to heat stress. Comparison of our data with results from previous microarray experiments revealed the importance of regulation of gene expression at the level of transcription of the most elevated proteins under heat shock conditions and enabled identification of several candidate genes whose expression may predominantly be regulated at the level of translation. This work demonstrates for the first time the use of a bioorthogonal amino acid for proteome-wide detection of changes in the amounts of proteins synthesized during a brief period upon variations in cellular growth conditions. Comparison of such data with relative mRNA levels enables assessment of the separate contributions of transcription and translation to the regulation of gene expression.

Labeling, detection and identification of newly synthesized proteomes with bioorthogonal non-canonical amino-acid tagging

A major aim of proteomics is the identification of proteins in a given proteome at a given metabolic state. This protocol describes the step-by-step labeling, purification and detection of newly synthesized proteins in mammalian cells using the non-canonical amino acid azidohomoalanine (AHA). In this method, metabolic labeling of newly synthesized proteins with AHA endows them with the unique chemical functionality of the azide group. In the subsequent click chemistry tagging reaction, azide-labeled proteins are covalently coupled to an alkyne-bearing affinity tag. After avidin-based affinity purification and on-resin trypsinization, the resulting peptide mixture is subjected to tandem mass spectrometry for identification. In combination with deuterated leucine-based metabolic colabeling, candidate proteins can be immediately validated. Bioorthogonal non-canonical amino-acid tagging can be combined with any subcellular fractionation, immunopurification or other proteomic method to identify specific subproteomes, thereby reducing sample complexity and enabling the identification of subtle changes in a proteome. This protocol can be completed in 5 days.

Fluorescence Visualization of Newly Synthesized Proteins in Mammalian Cells

Playing tag: Noncanonical amino acid tagging enables the selective fluorescent visualization of newly synthesized proteins in mammalian cells (see the picture). Susceptibility to tagging is determined by the spatial and temporal character of the protein synthesis, thus providing a complement to methods which identify relevant members of the proteome.

Selective identification of newly synthesized proteins in mammalian cells using bioorthogonal noncanonical amino acid tagging (BONCAT)

In both normal and pathological states, cells respond rapidly to environmental cues by synthesizing new proteins. The selective identification of a newly synthesized proteome has been hindered by the basic fact that all proteins, new and old, share the same pool of amino acids and thus are chemically indistinguishable. We describe here a technology, based on the cotranslational introduction of azide groups into proteins and the chemoselective tagging of azide-labeled proteins with an alkyne affinity tag, to separate and identify, specifically, the newly synthesized proteins in mammalian cells. Incorporation of the azide-bearing amino acid azidohomoalanine is unbiased, not toxic, and does not increase protein degradation. As a first demonstration of the method, we report the selective purification and identification of 195 metabolically labeled proteins with multidimensional liquid chromatography in-line with tandem MS. Furthermore, in combination with leucine-based mass tagging, candidates were immediately validated as newly synthesized proteins. The identified proteins, synthesized in a 2-h window, possess a broad range of biochemical properties and span most functional gene ontology categories. This technology makes it possible to address the temporal and spatial characteristics of newly synthesized proteomes in any cell type.