Small molecule substrates for the rapid quantification of acyl transfer activity of nylon hydrolase NylCA.

The widespread use of polyamides such as nylons has led to the accumulation of nylon waste, which is particularly resistant to decomposition due to the intrinsic stability of the amide bond. New methods are required for the true recycling of these waste materials by depolymerization. Enzymes that are capable of hydrolyzing polyamides have been proposed as biocatalysts that may be suitable for this application. NylC is an enzyme that can mediate the hydrolysis of aminohexanoic acid oligomers, and to some extent, bulk polymers. However, current assays to characterize the activity of this enzyme require long reaction times and/or rely on secondary reactions to quantify hydrolysis. Herein, we have designed structurally-optimized small molecule chromogenic esters that serve as substrate analogues for monitoring NylC acyltransferase activity in a continuous manner. This assay can be performed in minutes at room temperature, and the substrate N-acetyl-GABA-pNP ester (kcat = 0.37 s-1, KM = 256 µM) shows selectivity for NylC in complex biological media. We also demonstrate that activity towards this substrate analogue correlates with amide hydrolysis, which is the primary activity of this enzyme. Furthermore, our screening of substrate analogues provides insight into the substrate specificity of NylC, which is relevant to biocatalytic applications.

Refinement of the Fusion Tag PagP for Effective Formation of Inclusion Bodies in Escherichia coli.

Methods for efficient insoluble protein production require further exploration. PagP, an Escherichia coli outer membrane protein with high ß-sheet content, could function as an efficient fusion partner for inclusion body-targeted expression of recombinant peptides. The primary structure of a given polypeptide determines to a large extent its propensity to aggregate. Herein, aggregation "hot spots" (HSs) in PagP were analyzed using the web-based software AGGRESCAN, leading to identification of a C-terminal region harboring numerous HSs. Moreover, a proline-rich region was found in the ß-strands. Substitution of these prolines by residues with high ß-sheet propensity and hydrophobicity significantly improved its ability to form aggregates. Consequently, the absolute yields of recombinant antimicrobial peptides Magainin II, Metchnikowin, and Andropin were increased significantly when expressed in fusion with this refined version of PagP. We describe separation of recombinant target proteins expressed in inclusion bodies fused with the tag. An artificial NHT linker peptide with three motifs was implemented for separation and purification of authentic recombinant antimicrobial peptides. IMPORTANCE Fusion tag-induced formation of inclusion bodies provides a powerful means to express unstructured or toxic proteins. For a given fusion tag, how to enhance the formation of inclusion bodies remains to be explored. Our study illustrated that the aggregation HSs in a fusion tag played important roles in mediating its insoluble expression. Efficient production of inclusion bodies could also be implemented by refining its primary structure to form a more stable ß-sheet with higher hydrophobicity. This study provides a promising method for improvement of the insoluble expression of recombinant proteins.

High-Throughput Enzyme Assay for Screening Inhibitors of the ZDHHC3/7/20 Acyltransferases.

As enzymes that mediate the attachment of long-chain fatty acids to cysteine residues, ZDHHC proteins have been reported to be promising therapeutic targets for treating cancer and autoimmune diseases. Yet, due to the lack of potent selective inhibitors, scrutiny of the biological functions of ZDHHCs has been limited. The main hindrance for developing ZDHHC inhibitors is the lack of a facile high-throughput assay. Here, we developed a ZDHHC3/7/20 high-throughput assay based on the acylation-coupled lipophilic induction of polarization (Acyl-cLIP) method and screened several potential ZDHHC inhibitors. Furthermore, we demonstrated that in vitro results from the Acyl-cLIP assay are supported by the results from cell-based assays. We envision that this new ZDHHC3/7/20 Acyl-cLIP assay will accelerate the high-throughput screening of large compound libraries for improved ZDHHC inhibitors and provide therapeutic benefits for cancer and autoimmune diseases.

Identification of four secondary acyltransferases for lipid A biosynthesis in Vibrio parahaemolyticus.

In this study, four genes encoding secondary acyltransferases of lipid A in Vibrio parahaemolyticus ATCC33846 were identified. When the four genes were overexpressed in Escherichia coli MLK1067 that which produces the penta-acylated lipid A lacking the secondary acylation at the C3' position, a C12:0 secondary acyl chain was added at the C3' position of lipid A only in E. coli overexpressing VP_RS01045, but not VP_RS00880, VP_RS08405, or VP_RS12170. When the four genes were overexpressed in E. coli MKV15b that produces lipid IVA , a C12:0 secondary acyl chain was again added at the C3' position in E. coli overexpressing VP_RS01045, but a C14:0 secondary acyl chain was added at the C2' position of lipid A in E. coli overexpressing VP_RS00880, VP_RS08405, or VP_RS12170. The results indicate that four acyltransferases of lipid A are encoded by VP_RS01045, VP_RS00880, VP_RS08405, or VP_RS12170 in V. parahaemolyticus. The acyltransferase encoded by VP_RS01045 adds a C12:0 secondary acyl chain at the C3' position of lipid A, whereas the acyltransferase encoded by VP_RS00880, VP_RS08405, or VP_RS12170 adds a C14:0 secondary acyl chain at the C2' position of lipid A. This work contributes to understanding the biosynthetic pathway of lipid A in V. parahaemolyticus.

Regulatory effects of post-translational modifications on zDHHC S-acyltransferases.

The human zDHHC S-acyltransferase family comprises 23 enzymes that mediate the S-acylation of a multitude of cellular proteins, including channels, receptors, transporters, signaling molecules, scaffolds, and chaperones. This reversible post-transitional modification (PTM) involves the attachment of a fatty acyl chain, usually derived from palmitoyl-CoA, to specific cysteine residues on target proteins, which affects their stability, localization, and function. These outcomes are essential to control many processes, including synaptic transmission and plasticity, cell growth and differentiation, and infectivity of viruses and other pathogens. Given the physiological importance of S-acylation, it is unsurprising that perturbations in this process, including mutations in ZDHHC genes, have been linked to different neurological pathologies and cancers, and there is growing interest in zDHHC enzymes as novel drug targets. Although zDHHC enzymes control a diverse array of cellular processes and are associated with major disorders, our understanding of these enzymes is surprisingly incomplete, particularly with regard to the regulatory mechanisms controlling these enzymes. However, there is growing evidence highlighting the role of different PTMs in this process. In this review, we discuss how PTMs, including phosphorylation, S-acylation, and ubiquitination, affect the stability, localization, and function of zDHHC enzymes and speculate on possible effects of PTMs that have emerged from larger screening studies. Developing a better understanding of the regulatory effects of PTMs on zDHHC enzymes will provide new insight into the intracellular dynamics of S-acylation and may also highlight novel approaches to modulate S-acylation for clinical gain.

Antibody Fc Glycosylation Discriminates Between Latent and Active Tuberculosis.

BACKGROUND: Mycobacterium tuberculosis remains a global health problem and clinical management is complicated by difficulty in discriminating between latent infection and active disease. While M. tuberculosis-reactive antibody levels are heterogeneous, studies suggest that levels of IgG glycosylation differ between disease states. Here we extend this observation across antibody domains and M. tuberculosis specificities to define changes with the greatest resolving power. METHODS: Capillary electrophoretic glycan analysis was performed on bulk non-antigen-specific IgG, bulk Fc domain, bulk Fab domain, and purified protein derivative (PPD)- and Ag85A-specific IgG from subjects with latent (n = 10) and active (n = 20) tuberculosis. PPD-specific isotype/subclass, PPD-specific antibody-dependent phagocytosis, cellular cytotoxicity, and natural killer cell activation were assessed. Discriminatory potentials of antibody features were evaluated individually and by multivariate analysis. RESULTS: Parallel profiling of whole, Fc, and Fab domain-specific IgG glycosylation pointed to enhanced differential glycosylation on the Fc domain. Differential glycosylation was observed across antigen-specific antibody populations. Multivariate modeling highlighted Fc domain glycan species as the top discriminatory features, with combined PPD IgG titers and Fc domain glycans providing the highest classification accuracy. CONCLUSIONS: Differential glycosylation occurs preferentially on the Fc domain, providing significant discriminatory power between different states of M. tuberculosis infection and disease.

First access to a mycolic acid-based bioorthogonal reporter for the study of the mycomembrane and mycoloyltransferases in Corynebacteria.

In this study, we report the first synthesis of an alkyne-based trehalose monomycolate probe containing a ß-hydroxylated fatty acid and an α-branched chain similar to those of the natural mycolic acid. We demonstrate its utility for the labeling of the mycomembrane of Corynebacteria as well as for the study of mycoloyltransferases.

A Fluorescence-Based Assay for Quantitative Analysis of Phospholipid:Diacylglycerol Acyltransferase Activity.

Phospholipid:diacylglycerol acyltransferase (PDAT) catalyzes the acyl-CoA-independent triacylglycerol (TAG) biosynthesis in plants and oleaginous microorganisms and thus is a key target in lipid research. The conventional in vitro PDAT activity assay involves the use of radiolabeled substrates, which, however, are expensive and demand strict regulation. In this study, a reliable fluorescence-based method using nitrobenzoxadiazole-labeled diacylglycerol (NBD-DAG) as an alternative substrate was established and subsequently used to characterize the enzyme activity and kinetics of a recombinant Arabidopsis thaliana PDAT1 (AtPDAT1). We also demonstrate that the highly toxic benzene used in typical PDAT assays can be substituted with diethyl ether without affecting the formation rate of NBD-TAG. Overall, this method works well with a broad range of PDAT protein content and shows linear correlation with the conventional method with radiolabeled substrates, and thus may be applicable to PDAT from various plant and microorganism species.

PIGU overexpression adds value to TNM staging in the prognostic stratification of patients with hepatocellular carcinoma.

Phosphatidylinositol glycan anchor biosynthesis class U (PIGU), which is a critical subunit of the glycosylphosphatidylinositol transamidase (GPI-T) complex, has been reported to be an oncogene in bladder cancer. However, the expression and prognostic significance of PIGU in hepatocellular carcinoma (HCC) remain unclear. In this study, we conducted bioinformatics, quantitative real-time polymerase chain reaction, and immunohistochemistry analysis to investigate the expression profile of GPI-T subunits in HCC tissues, finding that PIGU was the most significantly overexpressed GPI-T subunit in HCC tissues at both the RNA and protein levels. Using Kaplan-Meier analysis and Cox proportional hazards regression models, we then comprehensively explored the prognostic impact of overexpressed PIGU in HCC patients in 2 independent HCC cohorts, and the results showed that overexpressed PIGU was an independent predictor for poor survival in HCC patients. Furthermore, based on the constructed nomogram, we proposed a risk score combining PIGU expression with the standard TNM staging system and provided a more powerful tool for the prognostic stratification of HCC patients. We also investigated the potential functional role of PIGU in HCC by performing bioinformatic analysis, indicating that PIGU might be involved in cell cycle-related biological processes in HCC. In conclusion, our findings suggest that PIGU overexpression provides independent and complementary prognostic information in HCC patients and that incorporation of this information with the traditional TNM staging system can improve prognostic stratification.

The determination of the infectious status and prevalence of motile Aeromonas species isolated from disease cases in rainbow trout (Oncorhynchus mykiss) and aquarium fish.

The aims of this study were to determine the prevalence and phylogenetic relationship of motile Aeromonas spp. that might be pathogenic species for rainbow trout in infected/mix infection cases (based upon different outbreaks on fish farms). A total of 99 motile Aeromonas isolates (and three reference strains) were analysed that were isolated from four different fish species in different sizes of fish (0.1-3,000 g), different months and water temperatures (6.1-21.2°C). The biochemical characteristics of the isolates were determined using conventional tests and a rapid test kit. Additionally, molecular identification was performed using the gyrB housekeeping gene region and with glycerophospholipid-cholesterol acyltransferase polymerase chain reaction (GCAT-PCR). The sequencing results obtained from the gyrB gene region were deposited in the GenBank database, and phylogenetic relationships were determined with the BioNumerics 7.6 database. Nearly half of the Aeromonas isolates that were isolated from rainbow trout showing signs of disease were determined to be possible infectious agents. Aeromonas species exhibit biochemical variability for many characters, so some Aeromonas species tested negative for GCAT-PCR despite that this test was created especially for Aeromonas identification. The phylogenetic tree based upon gyrB contained 10 different phylogroups that were based on 96% cut-off value in gyrB gene region.

Potential of High-Affinity, Slow Off-Rate Modified Aptamer Reagents for Mycobacterium tuberculosis Proteins as Tools for Infection Models and Diagnostic Applications.

Direct pathogen detection in blood to diagnose active tuberculosis (TB) has been difficult due to low levels of circulating antigens or due to the lack of specific, high-affinity binding reagents and reliable assays with adequate sensitivity. We sought to determine whether slow off-rate modified aptamer (SOMAmer) reagents with subnanomolar affinity for Mycobacterium tuberculosis proteins (antigens 85A, 85B, 85C, GroES, GroEL2, DnaK, CFP10, KAD, CFP2, RplL, and Tpx) could be useful to diagnose tuberculosis. When incorporated into the multiplexed, array-based proteomic SOMAscan assay, limits of detection reached the subpicomolar range in 40% serum. Binding to native M. tuberculosis proteins was confirmed by using M. tuberculosis culture filtrate proteins and fractions from infected macrophages and via affinity capture assays and subsequent mass spectrometry. Comparison of serum from culture-positive pulmonary TB patients and TB suspects systematically ruled out for TB revealed small but statistically significant (P < 0.0001) differences in the median M. tuberculosis signals and in specific pathogen markers, such as antigen 85B. Samples where many M. tuberculosis aptamers produced high signals were rare exceptions. In concentrated, protein-normalized urine from TB patients and non-TB controls, the CFP10 (EsxB) SOMAmer yielded the most significant differential signals (P < 0.0276), particularly in TB patients with HIV coinfection. In conclusion, direct M. tuberculosis antigen detection proved difficult even with a sensitive method such as SOMAscan, likely due to their very low, subpicomolar abundance. The observed differences between cases and controls had limited diagnostic utility in serum and urine, but further evaluation of M. tuberculosis SOMAmers using other platforms and sample types is warranted.

MicroRNA-340-5p modulates cisplatin resistance by targeting LPAATß in osteosarcoma.

MicroRNAs (miRNAs) play an important role in drug resistance and modulate the efficiency of chemotherapy. A recent study indicated that miR-340 functions as a tumor suppressor in various types of cancer. However, the role of miR-340 in chemotherapy has not been reported yet. In this study, we found that miR-340 enhanced cisplatin (CDDP)-induced cell death. Induction of miR-340-5p expression decreased the IC50 of CDDP and increased the apoptosis of CDDP-resistant MG-63 and Saos-2 cells. Moreover, miR-340-5p decreased the accumulation of MRP1 and MDR1. We further explored the mechanism underlying the promoting effects of miR-340-5p on CDDP-induced cell death. We identified a potential target of miR-340 in the 3' untranslated region of lysophosphatidic acid acyltransferase (LPAATß) using the online program Targetscan (http://www.microrna.org). Luciferase reporter assays showed that miR-340 binds to the 3'UTR of LPAATß. Enforced expression of miR-340-5p decreased the accumulation of LPAATß in both MG-63 and Saos-2 cells. Silencing LPAATß decreased the IC50 of CDDP and increased the apoptosis of CDDP-resistant MG-63 and Saos-2 cells, which is consistent with the effect of miR-340-5p on CDDP-induced cell death. Moreover, induced expression of LPAATß compromised the effects of miR-340-5p on CDDP-induced cell death and accumulation of MRP1 and MDR1. Taken together, our data indicated that miR-340-5p enhanced the sensitivity to CDDP by targeting LPAATß.

An easy and sensitive sandwich assay for detection of Mycobacterium tuberculosis Ag85B antigen using quantum dots and gold nanorods.

Mycobacterium tuberculosis is a serious global infectious pathogen causing tuberculosis (TB). The development of an easy and sensitive method for the detection of M. tuberculosis is in urgent need due to complex and low specificity of the current assays. Herein, we present a novel method for M. tuberculosis detection based on a sandwich assay via antigen-antibody interaction using silica-coated quantum dots (SiQDs) and gold nanorods (AuNRs). A genetically engineered recombinant antibody (GBP-50B14 and SiBP-8B3) was bound to surfaces of AuNRs and SiQDs respectively, without any surface modification. The antigen-antibody interaction was revealed using M. tuberculosis-specific secretory antigen, Ag85B. Two biocomplexes showed a quenching effect in the presence of the target antigen through a sandwich assay. The assay response was in the range of 1×10-3-1×10-10µgmL-1 (R=0.969) and the limit of detection for Ag85B was 13.0pgmL-1. The Ag85B was selectively detected using three different proteins (CFP10, and BSA), and further specifically confirmed by the use of spiked samples. Compared with existing methods, a highly sensitive and selective method for Ag85B-expressing M. tuberculosis detection has been developed for better diagnosis of TB.

MicroRNA-340-5p modulates cisplatin resistance by targeting LPAATβ in osteosarcoma

MicroRNAs (miRNAs) play an important role in drug resistance and modulate the efficiency of chemotherapy. A recent study indicated that miR-340 functions as a tumor suppressor in various types of cancer. However, the role of miR-340 in chemotherapy has not been reported yet. In this study, we found that miR-340 enhanced cisplatin (CDDP)-induced cell death. Induction of miR-340-5p expression decreased the IC50 of CDDP and increased the apoptosis of CDDP-resistant MG-63 and Saos-2 cells. Moreover, miR-340-5p decreased the accumulation of MRP1 and MDR1. We further explored the mechanism underlying the promoting effects of miR-340-5p on CDDP-induced cell death. We identified a potential target of miR-340 in the 3′ untranslated region of lysophosphatidic acid acyltransferase (LPAATβ) using the online program Targetscan (http://www.microrna.org). Luciferase reporter assays showed that miR-340 binds to the 3′UTR of LPAATβ. Enforced expression of miR-340-5p decreased the accumulation of LPAATβ in both MG-63 and Saos-2 cells. Silencing LPAATβ decreased the IC50 of CDDP and increased the apoptosis of CDDP-resistant MG-63 and Saos-2 cells, which is consistent with the effect of miR-340-5p on CDDP-induced cell death. Moreover, induced expression of LPAATβ compromised the effects of miR-340-5p on CDDP-induced cell death and accumulation of MRP1 and MDR1. Taken together, our data indicated that miR-340-5p enhanced the sensitivity to CDDP by targeting LPAATβ.

A silicon nitride ISFET based immunosensor for Ag85B detection of tuberculosis.

A silicon nitride Ion Sensitive Field Effect Transistor (ISFET) based immunosensor was developed as a low-cost and label-free electrical detection for the detection of antigen 85 complex B (Ag85B). The sensing membrane of the ISFET was modified with 3-aminopropyltriethoxysilane (APTES) followed by glutaraldehyde (GA), yielding an aldehyde-terminated surface. This group is available for immobilization of a monoclonal antibody against a recombinant Ag85B protein (anti-Ag85B antibody). The optimal concentration for anti-Ag85B antibody immobilization onto the modified ISFET was 100 µg ml-1. This optimal condition provided the maximal binding capability and minimal non-specific background signal. The binding event between the recombinant Ag85B antigen and anti-Ag85B antibody on the ISFET surface is presented by monitoring the gate potential change at a constant drain current. The dose response for the recombinant Ag85B protein showed a linear response between 0.12 and 1 µg ml-1 without significant interference from other recombinant proteins. The analytical imprecision (CV%) and accuracy of this Ag85B protein biosensor were 9.73-10.99% and 95.29%, respectively. In addition, an irrelevant antibody and other recombinant proteins were employed as a negative control to demonstrate the non-specific interaction of the antigen and antibody. The success of this immunosensor system for Ag85B protein detection facilitates the construction of a promising device which can shorten the turnaround time for the diagnosis of tuberculosis compared to a standard culture method. Furthermore, this device could also be applied for real-time growth monitoring of Mycobacterium tuberculosis in a mycobacterial culture system.

Biochemical characterization of human acyl coenzyme A: 2-monoacylglycerol acyltransferase-3 (MGAT3).

BACKGROUND: MGAT3 catalyzes the synthesis of 1,2-diacylglycerol from 2-monoacylglycerol in an acyl CoA-dependent reaction. Although initially identified as an MGAT enzyme, MGAT3 is more closely related to DGAT2 than to MGAT1 and MGAT2. Furthermore, MGAT3 possesses both DGAT and MGAT activities, in vitro. MGAT3 is almost exclusively expressed in the small intestine in humans, suggesting that it has a role in dietary fat absorption. Although identified many years ago, little information is available regarding the contribution of MGAT3 to triacylglycerol biosynthesis. RESULTS: This study confirmed the initial observations that MGAT3 possessed both MGAT and DGAT activities. When expressed in cells in culture, MGAT3 stimulated lipid droplet growth, but unlike DGAT2, does not become concentrated around the lipid droplet surface. We also characterized the MGAT activity of an MGAT3 mutant in which a conserved cysteine was changed to a tyrosine residue. Lastly, although they share significant sequence identity, MGAT3 is a much more stable protein than DGAT2, yet they are both polyubiquitinated and degraded through ER-associated degradation by the proteasome. CONCLUSION: Our findings provide additional evidence that MGAT3 likely functions as a TG synthase in cells.

Polysorbates 20 and 80 Degradation by Group XV Lysosomal Phospholipase A2 Isomer X1 in Monoclonal Antibody Formulations.

Decreases in polysorbate (PS80) content were observed while evaluating the long-term storage stability of Chinese hamster ovary-derived, purified monoclonal antibodies. It was determined that polysorbate had been enzymatically degraded; therefore, studies were performed to identify and characterize the protein(s) responsible. Polysorbate degrading activity was enriched from Chinese hamster ovary media leading to the identification of group XV lysosomal phospholipase A2 isomer X1 (LPLA2) by shotgun proteomics. Recombinant LPLA2 was over expressed, purified, and functional integrity confirmed against a diheptanoyl phosphatidylcholine substrate. Incubation of recombinantly produced LPLA2 with PS20 and PS80 resulted in hydrolysis of PS20 and PS80 monoester but a much slower rate was observed for higher-order PS80. Endogenous LPLA2 was detected and quantitated at less than 1 ppm in 3 formulated antibodies while LPLA2 was not detected (or less than 0.1 ppm) in a fourth formulated antibody. Furthermore, antibodies with detectable quantities of endogenous LPLA2 demonstrated polysorbate hydrolysis while in contrast the antibody without detectable LPLA2 did not show polysorbate hydrolysis. Comparison of polysorbate degradation products generated from the formulated antibody and samples of polysorbate incubated with recombinant LPLA2 resulted in similar elution profiles by liquid chromatography-mass spectrometry. These results suggest that LPLA2 may play a key role in polysorbate degradation in some antibody preparations.

Diagnosis of pulmonary and extrapulmonary tuberculosis based on detection of mycobacterial antigen 85B by immuno-PCR.

We developed a novel indirect sandwich immuno-polymerase chain reaction (I-PCR) assay for the detection of mycobacterial antigen 85B (Ag85B, 30kDa, Rv1886c) in pulmonary tuberculosis (PTB) and extrapulmonary tuberculosis (EPTB) patients. The amino-modified reporter DNA was covalently attached with the antidetection antibody through a heterobifunctional cross-linking agent succinimidyl 4-[N-maleimidomethyl]-cyclohexane-1-carboxylate. The detection limit of Ag85B by I-PCR was found to be 1 femtogram (fg)/mL, which was 10(6)-fold lower than an analogous enzyme-linked immunosorbent assay (ELISA). The sensitivities of 85% and 77% with I-PCR and 77.6% and 62.5% with ELISA were observed in smear-positive and smear-negative PTB patients, respectively, with high specificity. On the other hand, sensitivities of 84% and 63.7% with I-PCR and 68% and 47.5% with ELISA were observed in confirmed and clinically suspected EPTB cases, respectively, with high specificity.

Mechanistic analysis of ghrelin-O-acyltransferase using substrate analogs.

Ghrelin-O-Acyltransferase (GOAT) is an 11-transmembrane integral membrane protein that octanoylates the metabolism-regulating peptide hormone ghrelin at Ser3 and may represent an attractive target for the treatment of type II diabetes and the metabolic syndrome. Protein octanoylation is unique to ghrelin in humans, and little is known about the mechanism of GOAT or of related protein-O-acyltransferases HHAT or PORC. In this study, we explored an in vitro microsomal ghrelin octanoylation assay to analyze its enzymologic features. Measurement of Km for 10-mer, 27-mer, and synthetic Tat-peptide-containing ghrelin substrates provided evidence for a role of charge interactions in substrate binding. Ghrelin substrates with amino-alanine in place of Ser3 demonstrated that GOAT can catalyze the formation of an octanoyl-amide bond at a similar rate compared with the natural reaction. A pH-rate comparison of these substrates revealed minimal differences in acyltransferase activity across pH 6.0-9.0, providing evidence that these reactions may be relatively insensitive to the basicity of the substrate nucleophile. The conserved His338 residue was required both for Ser3 and amino-Ala3 ghrelin substrates, suggesting that His338 may have a key catalytic role beyond that of a general base.

Global analysis of protein N-myristoylation and exploration of N-myristoyltransferase as a drug target in the neglected human pathogen Leishmania donovani.

N-Myristoyltransferase (NMT) modulates protein function through the attachment of the lipid myristate to the N terminus of target proteins, and is a promising drug target in eukaryotic parasites such as Leishmania donovani. Only a small number of NMT substrates have been characterized in Leishmania, and a global picture of N-myristoylation is lacking. Here, we use metabolic tagging with an alkyne-functionalized myristic acid mimetic in live parasites followed by downstream click chemistry and analysis to identify lipidated proteins in both the promastigote (extracellular) and amastigote (intracellular) life stages. Quantitative chemical proteomics is used to profile target engagement by NMT inhibitors, and to define the complement of N-myristoylated proteins. Our results provide new insight into the multiple pathways modulated by NMT and the pleiotropic effects of NMT inhibition. This work constitutes the first global experimental analysis of protein lipidation in Leishmania, and reveals the extent of NMT-related biology yet to be explored for this neglected human pathogen.