Preparation of the functionalizable methionine surrogate azidohomoalanine via copper-catalyzed diazo transfer

Subcellular sequencing of single neurons reveals the dendritic transcriptome of GABAergic interneurons

Although mRNAs are localized in the processes of excitatory neurons, it is still unclear whether interneurons also localize a large population of mRNAs. In addition, the variability in the localized mRNA population within and between cell types is unknown. Here we describe the unbiased transcriptomic characterization of the subcellular compartments of hundreds of single neurons. We separately profiled the dendritic and somatic transcriptomes of individual rat hippocampal neurons and investigated mRNA abundances in the soma and dendrites of single glutamatergic and GABAergic neurons. We found that, like their excitatory counterparts, interneurons contain a rich repertoire of ~4000 mRNAs. We observed more cell type-specific features among somatic transcriptomes than their associated dendritic transcriptomes. Finally, using celltype-specific metabolic labeling of isolated neurites, we demonstrated that the processes of glutamatergic and, notably, GABAergic neurons were capable of local translation, suggesting mRNA localization and local translation are general properties of neurons.

Directed Evolution Using Stabilized Bacterial Peptide Display

Chemically stabilized peptides have attracted intense interest by academics and pharmaceutical companies due to their potential to hit currently "undruggable" targets. However, engineering an optimal sequence, stabilizing linker location, and physicochemical properties is a slow and arduous process. By pairing non-natural amino acid incorporation and cell surface click chemistry in bacteria with high-throughput sorting, we developed a method to quantitatively select high affinity ligands and applied the Stabilized Peptide Evolution by E. coli Display technique to develop disrupters of the therapeutically relevant MDM2-p53 interface. Through in situ stabilization on the bacterial surface, we demonstrate rapid isolation of stabilized peptides with improved affinity and novel structures. Several peptides evolved a second loop including one sequence (K_d = 1.8 nM) containing an i, i+4 disulfide bond. NMR structural determination indicated a bent helix in solution and bound to MDM2. The bicyclic peptide had improved protease stability, and we demonstrated that protease resistance could be measured both on the bacterial surface and in solution, enabling the method to test and/or screen for additional drug-like properties critical for biologically active compounds.

Altered steady state and activity-dependent de novo protein expression in fragile X syndrome

Whether fragile X mental retardation protein (FMRP) target mRNAs and neuronal activity contributing to elevated basal neuronal protein synthesis in fragile X syndrome (FXS) is unclear. Our proteomic experiments reveal that the de novo translational profile in FXS model mice is altered at steady state and in response to metabotropic glutamate receptor (mGluR) stimulation, but the proteins expressed differ under these conditions. Several altered proteins, including Hexokinase 1 and Ras, also are expressed in the blood of FXS model mice and pharmacological treatments previously reported to ameliorate phenotypes modify their abundance in blood. In addition, plasma levels of Hexokinase 1 and Ras differ between FXS patients and healthy volunteers. Our data suggest that brain-based de novo proteomics in FXS model mice can be used to find altered expression of proteins in blood that could serve as disease-state biomarkers in individuals with FXS.

Elevated protein synthesis, and dysregulated mGluR signalling, are documented in fragile X syndrome (FXS) Here the authors use proteomic analysis in a mouse model of FXS, and following mGluR5 stimulation, to identify potential biomarkers for the disease.

Nonradioactive quantification of autophagic protein degradation with L-azidohomoalanine labeling

At present, several assays that use radioisotope labeling to quantify the degradation of long-lived proteins have been developed to measure autophagic flux. Here, we describe a nonradioactive pulse-chase protocol using L-azidohomoalanine (AHA) labeling to quantify long-lived protein degradation during autophagy. AHA is used as a surrogate for L-methionine, and, when added to cultured cells grown in methionine-free medium, AHA is incorporated into proteins during de novo protein synthesis. After a chase period to remove short-lived proteins, autophagy is induced by starvation or other stimuli. Cells then undergo a 'click' reaction between the azide group of AHA and a fluorescently tagged alkyne probe. The AHA-containing proteins can then be detected by flow cytometry. This protocol is nonradioactive, sensitive and quantitative, and it is easy to perform. It is also applicable to various cell culture systems. The whole protocol is estimated to take 4-5 d to complete.

SutA is a bacterial transcription factor expressed during slow growth in Pseudomonas aeruginosa

Microbial quiescence and slow growth are ubiquitous physiological states, but their study is complicated by low levels of metabolic activity. To address this issue, we used a time-selective proteome-labeling method [bioorthogonal noncanonical amino acid tagging (BONCAT)] to identify proteins synthesized preferentially, but at extremely low rates, under anaerobic survival conditions by the opportunistic pathogen Pseudomonas aeruginosa. One of these proteins is a transcriptional regulator that has no homology to any characterized protein domains and is posttranscriptionally up-regulated during survival and slow growth. This small, acidic protein associates with RNA polymerase, and chromatin immunoprecipitation (ChIP) followed by high-throughput sequencing suggests that the protein associates with genomic DNA through this interaction. ChIP signal is found both in promoter regions and throughout the coding sequences of many genes and is particularly enriched at ribosomal protein genes and in the promoter regions of rRNA genes. Deletion of the gene encoding this protein affects expression of these and many other genes and impacts biofilm formation, secondary metabolite production, and fitness in fluctuating conditions. On the basis of these observations, we have designated the protein SutA (survival under transitions A).

Time-resolved proteomic analysis of quorum sensing in Vibrio harveyi

Bacteria use a process of chemical communication called quorum sensing to assess their population density and to change their behavior in response to fluctuations in the cell number and species composition of the community. In this work, we identified the quorum-sensing-regulated proteome in the model organism Vibrio harveyi by bio-orthogonal non-canonical amino acid tagging (BONCAT). BONCAT enables measurement of proteome dynamics with temporal resolution on the order of minutes. We deployed BONCAT to characterize the time-dependent transition of V. harveyi from individual- to group-behaviors. We identified 176 quorum-sensing-regulated proteins at early, intermediate, and late stages of the transition, and we mapped the temporal changes in quorum-sensing proteins controlled by both transcriptional and post-transcriptional mechanisms. Analysis of the identified proteins revealed 86 known and 90 new quorum-sensing-regulated proteins with diverse functions, including transcription factors, chemotaxis proteins, transport proteins, and proteins involved in iron homeostasis.

Cell-selective labelling of proteomes in Drosophila melanogaster

The specification and adaptability of cells rely on changes in protein composition. Nonetheless, uncovering proteome dynamics with cell-type-specific resolution remains challenging. Here we introduce a strategy for cell-specific analysis of newly synthesized proteomes by combining targeted expression of a mutated methionyl-tRNA synthetase (MetRS) with bioorthogonal or fluorescent non-canonical amino-acid-tagging techniques (BONCAT or FUNCAT). Substituting leucine by glycine within the MetRS-binding pocket (MetRS^LtoG) enables incorporation of the non-canonical amino acid azidonorleucine (ANL) instead of methionine during translation. Newly synthesized proteins can thus be labelled by coupling the azide group of ANL to alkyne-bearing tags through ‘click chemistry'. To test these methods for applicability in vivo, we expressed MetRS^LtoG cell specifically in Drosophila. FUNCAT and BONCAT reveal ANL incorporation into proteins selectively in cells expressing the mutated enzyme. Cell-type-specific FUNCAT and BONCAT, thus, constitute eligible techniques to study protein synthesis-dependent processes in complex and behaving organisms.

Mutated tRNA synthetases can incorporate non-canonical amino acids into proteins. Erdmann et al. exploit this property to metabolically label newly synthesized proteins in selected cell types in Drosophila, and demonstrate their detection using proteomics (BONCAT) and fluorescence imaging (FUNCAT).

Direct visualization of newly synthesized target proteins in situ

Protein synthesis is a dynamic process that tunes the cellular proteome in response to internal and external demands. Metabolic labeling approaches identify the general proteomic response but cannot visualize specific newly synthesized proteins within cells. Here we describe a technique that couples noncanonical amino acid tagging or puromycylation with the proximity ligation assay to visualize specific newly synthesized proteins and monitor their origin, redistribution and turnover in situ.

In-depth quantitative proteomic analysis of de novo protein synthesis induced by brain-derived neurotrophic factor

Measuring the synthesis of new proteins in the context of a much greater number of pre-existing proteins can be difficult. To overcome this obstacle, bioorthogonal noncanonical amino acid tagging (BONCAT) can be combined with stable isotope labeling by amino acid in cell culture (SILAC) for comparative proteomic analysis of de novo protein synthesis (BONLAC). In the present study, we show that alkyne resin-based isolation of l-azidohomoalanine (AHA)-labeled proteins using azide/alkyne cycloaddition minimizes contamination from pre-existing proteins. Using this approach, we isolated and identified 7414 BONCAT-labeled proteins. The nascent proteome isolated by BONCAT was very similar to the steady-state proteome, although transcription factors were highly enriched by BONCAT. About 30% of the methionine residues were replaced by AHA in our BONCAT samples, which allowed for identification of methionine-containing peptides. There was no bias against low-methionine proteins by BONCAT at the proteome level. When we applied the BONLAC approach to screen for brain-derived neurotrophic factor (BDNF)-induced protein synthesis, 53 proteins were found to be significantly changed 2 h after BDNF stimulation. Our study demonstrated that the newly synthesized proteome, even after a short period of stimulation, can be efficiently isolated by BONCAT and analyzed to a depth that is similar to that of the steady-state proteome.

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 ((15)NH(3) assimilation) for individual cells within a sediment-sourced enrichment culture showed concordance between AHA-positive cells and (15)N 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.

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 ((15)NH(3) assimilation) for individual cells within a sediment-sourced enrichment culture showed concordance between AHA-positive cells and (15)N 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.

Coupling bioorthogonal chemistries with artificial metabolism: intracellular biosynthesis of azidohomoalanine and its incorporation into recombinant proteins

In this paper, we present a novel, “single experiment” methodology based on genetic engineering of metabolic pathways for direct intracellular production of non-canonical amino acids from simple precursors, coupled with expanded genetic code. In particular, we engineered the intracellular biosynthesis of l-azidohomoalanine from O-acetyl-l-homoserine and NaN₃, and achieved its direct incorporation into recombinant target proteins by AUG codon reassignment in a methionine-auxotroph E. coli strain. In our system, the host’s methionine biosynthetic pathway was first diverted towards the production of the desired non-canonical amino acid by exploiting the broad reaction specificity of recombinant pyridoxal phosphate-dependent O-acetylhomoserine sulfhydrylase from Corynebacterium glutamicum. Then, the expression of the target protein barstar, accompanied with efficient l-azidohomoalanine incorporation in place of l-methionine, was accomplished. This work stands as proof-of-principle and paves the way for additional work towards intracellular production and site-specific incorporation of biotechnologically relevant non-canonical amino acids directly from common fermentable sources.

Deubiquitinating enzyme specificity for ubiquitin chain topology profiled by di-ubiquitin activity probes

Posttranslational modification with ubiquitin (Ub) controls many cellular processes, and aberrant ubiquitination can contribute to cancer, immunopathology, and neurodegeneration. The versatility arises from the ability of Ub to form polymer chains with eight distinct linkages via lysine side chains and the N terminus. In this study, we engineered Di-Ub probes mimicking all eight different poly-Ub linkages and profiled the deubiquitinating enzyme (DUB) selectivity for recognizing Di-Ub moieties in cellular extracts. Mass spectrometric profiling revealed that most DUBs examined have broad selectivity, whereas a subset displays a clear preference for recognizing noncanonical over K48/K63 Ub linkages. Our results expand knowledge of Ub processing enzyme functions in cellular contexts that currently depends largely on using recombinant enzymes and substrates.

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Synthesis of Di-ubiquitin-based active site probes representing all eight linkages

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Mass spectrometric profiling of DUB-Ub linkage preference in whole cell extracts

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Activity-based Di-Ub probe screen for DUB specificity toward poly-Ub linkages

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DUBs detected with a preference for noncanonical linkages over K48/K63-linked Ub

Dopaminergic modulation of the hippocampal neuropil proteome identified by bioorthogonal noncanonical amino acid tagging (BONCAT)

Local protein synthesis and its activity-dependent modulation via dopamine receptor stimulation play an important role in synaptic plasticity - allowing synapses to respond dynamically to changes in their activity patterns. We describe here the metabolic labeling, enrichment, and MS-based identification of candidate proteins specifically translated in intact hippocampal neuropil sections upon treatment with the selective D1/D5 receptor agonist SKF81297. Using the noncanonical amino acid azidohomoalanine and click chemistry, we identified over 300 newly synthesized proteins specific to dendrites and axons. Candidates specific for the SKF81297-treated samples were predominantly involved in protein synthesis and synapse-specific functions. Furthermore, we demonstrate a dendrite-specific increase in proteins synthesis upon application of SKF81297. This study provides the first snapshot in the dynamics of the dopaminergic hippocampal neuropil proteome.

Metabolic labeling with noncanonical amino acids and visualization by chemoselective fluorescent tagging

Fluorescent labeling of proteins by genetically encoded fluorescent protein tags has enabled an enhanced understanding of cell biological processes but is restricted to the analysis of a limited number of identified proteins. This approach does not permit, e.g., the unbiased visualization of a full proteome in situ. We describe here a fluorescence-based method to follow proteome-wide patterns of newly synthesized proteins in cultured cells, tissue slices, and a whole organism. This technique is compatible with immunohistochemistry and in situ hybridization. Key to this method is the introduction of a small bio-orthogonal reactive group by metabolic labeling. This is accomplished by replacing the amino acid methionine by the azide-bearing methionine surrogate azidohomoalanine (AHA) in a step very similar to classical radioisotope labeling. Subsequently, an alkyne-bearing fluorophore is covalently attached to the group by "click chemistry"--a copper(I)-catalyzed [3+2]azide-alkyne cycloaddition. By similar means, metabolic labeling can also be performed with the alkyne-bearing homopropargylglycine (HPG) and clicked to an azide-functionalized fluorophore.

Chemoselective modification of viral surfaces via bioorthogonal click chemistry

The modification of virus particles has received a significant amount of attention for its tremendous potential for impacting gene therapy, oncolytic applications and vaccine development. Current approaches to modifying viral surfaces, which are mostly genetics-based, often suffer from attenuation of virus production, infectivity and cellular transduction. Using chemoselective click chemistry, we have developed a straightforward alternative approach which sidesteps these issues while remaining both highly flexible and accessible. The goal of this protocol is to demonstrate the effectiveness of using bioorthogonal click chemistry to modify the surface of adenovirus type 5 particles. This two-step process can be used both therapeutically or analytically, as it allows for chemoselective ligation of targeting molecules, dyes or other molecules of interest onto proteins pre-labeled with azide tags. The three major advantages of this method are that (1) metabolic labeling demonstrates little to no impact on viral fitness, (2) a wide array of effector ligands can be utilized, and (3) it is remarkably fast, reliable and easy to access. In the first step of this procedure, adenovirus particles are produced bearing either azidohomoalanine (Aha, a methionine surrogate) or the unnatural sugar O-linked N-azidoacetylglucosamine (O-GlcNAz), both of which contain the azide (-N3) functional group. After purification of the azide-modified virus particles, an alkyne probe containing the fluorescent TAMRA moiety is ligated in a chemoselective manner to the pre-labeled proteins or glycoproteins. Finally, an SDS-PAGE analysis is performed to demonstrate the successful ligation of the probe onto the viral capsid proteins. Aha incorporation is shown to label all viral capsid proteins (Hexon, Penton and Fiber), while O-GlcNAz incorporation results in labeling of Fiber only. In this evolving field, multiple methods for azide-alkyne ligation have been successfully developed; however only the two we have found to be most convenient are demonstrated herein - strain-promoted azide-alkyne cycloaddition (SPAAC) and copper-catalyzed azide-alkyne cycloaddition (CuAAC) under deoxygenated atmosphere.

State-selective metabolic labeling of cellular proteins

Transcriptional activity from a specified promoter can provide a useful marker for the physiological state of a cell. Here we introduce a method for selective tagging of proteins made in cells in which specified promoters are active. Tagged proteins can be modified with affinity reagents for enrichment or with fluorescent dyes for visualization. The method allows state-selective analysis of the proteome, whereby proteins synthesized in predetermined physiological states can be identified. The approach is demonstrated by proteome-wide labeling of bacterial proteins upon activation of the P(BAD) promoter and the SoxRS regulon and provides a basis for analysis of more complex systems including spatially heterogeneous microbial cultures and biofilms.

Two-strain, cell-selective protein labeling in mixed bacterial cultures

Cell-selective metabolic labeling of proteins with noncanonical amino acids enables the study of proteomic changes in specified subpopulations of complex multicellular systems. For example, azidonorleucine (Anl) and 2-aminooctynoic acid, both of which are activated by an engineered methionyl-tRNA synthetase (designated NLL-MetRS), are excluded from proteins made in wild-type cells but incorporated readily into proteins made in cells that carry NLL-MetRS. To expand the set of tools available for cell-selective metabolic labeling, we sought a MetRS variant capable of activating propargylglycine (Pra). Pra was chosen as the target amino acid because its alkynyl side chain can be selectively and efficiently conjugated to azide-functionalized fluorescence probes and affinity tags. Directed evolution, using active-site randomization and error-prone PCR, yielded a MetRS variant (designated PraRS) capable of incorporating Pra at near-quantitative levels into proteins made in a Met-auxotrophic strain of Escherichia coli cultured in Met-depleted media. Proteins made in E. coli strains expressing PraRS were labeled with Pra in Met-supplemented media as shown by in-gel fluorescence after conjugation to Cy5-azide. The combined use of NLL-MetRS and PraRS enabled differential, cell-selective labeling of marker proteins derived from two bacterial strains cocultured in media supplemented with Met, Anl, and Pra. Treatment of the mixed marker proteins by sequential strain-promoted and copper(I)-catalyzed cycloadditions allowed straightforward identification of the cellular origin of each protein.

Non-canonical amino acid labeling in vivo to visualize and affinity purify newly synthesized proteins in larval zebrafish

Protein expression in the nervous system undergoes regulated changes in response to changes in behavioral states, in particular long-term memory formation. Recently, methods have been developed (BONCAT and FUNCAT), which introduce non-canonical amino acids bearing small bio-orthogonal functional groups into proteins using the cells' own translational machinery. Using the selective 'click reaction', this allows for the identification and visualization of newly synthesized proteins in vitro. Here we demonstrate that non-canonical amino acid labeling can be achieved in vivo in an intact organism capable of simple learning behavior, the larval zebrafish. We show that azidohomoalanine is metabolically incorporated into newly synthesized proteins, in a time- and concentration-dependent manner, but has no apparent toxic effect and does not influence simple behaviors such as spontaneous swimming and escape responses. This enables fluorescent labeling of newly synthesized proteins in whole mount larval zebrafish. Furthermore, stimulation with a GABA antagonist that elicits seizures in the larval zebrafish causes an increase in protein synthesis throughout the proteome, which can also be visualized in intact larvae.

Formation of ubiquitin dimers via azide-alkyne click reaction

The conjugation of poly-ubiquitin chains is a widespread post-translational modification of proteins that plays a role in many different cellular processes. Notably, the biological function of the attached ubiquitin chain depends on which lysine residue is used for chain formation. Here, we report a method for the modular synthesis of site-specifically linked ubiquitin dimers, which is based on click reaction between two artificial amino acids. In this way, it is possible to synthesize all seven naturally occurring ubiquitin connectivities, thus giving access to all ubiquitin dimers. Furthermore, this method can be generally applied to link ubiquitin to any substrate protein or even to link any two proteins site specifically.

Cleavable biotin probes for labeling of biomolecules via azide-alkyne cycloaddition

The azide-alkyne cycloaddition provides a powerful tool for bio-orthogonal labeling of proteins, nucleic acids, glycans, and lipids. In some labeling experiments, e.g., in proteomic studies involving affinity purification and mass spectrometry, it is convenient to use cleavable probes that allow release of labeled biomolecules under mild conditions. Five cleavable biotin probes are described for use in labeling of proteins and other biomolecules via azide-alkyne cycloaddition. Subsequent to conjugation with metabolically labeled protein, these probes are subject to cleavage with either 50 mM Na(2)S(2)O(4), 2% HOCH(2)CH(2)SH, 10% HCO(2)H, 95% CF(3)CO(2)H, or irradiation at 365 nm. Most strikingly, a probe constructed around a dialkoxydiphenylsilane (DADPS) linker was found to be cleaved efficiently when treated with 10% HCO(2)H for 0.5 h. A model green fluorescent protein was used to demonstrate that the DADPS probe undergoes highly selective conjugation and leaves a small (143 Da) mass tag on the labeled protein after cleavage. These features make the DADPS probe especially attractive for use in biomolecular labeling and proteomic studies.

A concise and scalable route to L-azidohomoalanine

A concise and highly efficient synthetic route to L-azidohomoalanine (L-Aha) and its homologues is presented here. These chemically modified amino acids are used for the introduction of bioorthogonal handles into proteins. The described route avoids major problems of previously reported methods including expensive starting materials, low efficiency, and lack of scalability. Starting from inexpensive N-Boc-O-Bn-L-aspartic acid, gram quantities of L-Aha hydrochloride can be prepared with high purity. The reactions can be completed within 1 week and the products can be incorporated into proteins using L-methionine auxotrophs.

Unnatural amino acid incorporation into virus-like particles

Virus-like particles composed of hepatitis B virus (HBV) or bacteriophage Qbeta capsid proteins have been labeled with azide- or alkyne-containing unnatural amino acids by expression in a methionine auxotrophic strain of E. coli. The substitution does not affect the ability of the particles to self-assemble into icosahedral structures indistinguishable from native forms. The azide and alkyne groups were addressed by Cu(I)-catalyzed [3 + 2] cycloaddition: HBV particles were decomposed by the formation of more than 120 triazole linkages per capsid in a location-dependent manner, whereas Qbeta suffered no such instability. The marriage of these well-known techniques of sense-codon reassignment and bioorthogonal chemical coupling provides the capability to construct polyvalent particles displaying a wide variety of functional groups with near-perfect control of spacing.

Synthesis of the functionalizable methionine surrogate azidohomoalanine using Boc-homoserine as precursor

This protocol describes a synthetic route to the non-canonical amino acid azidohomoalanine (AHA) using protected homoserine as a starting material. An alternative route to AHA is presented in a companion paper. This synthesis can be completed in 5 days.