An efficient system for bioconjugation based on a widely applicable engineered O-glycosylation tag.

Bioconjugates are an important class of therapeutic molecules. To date, O-glycan-based metabolic glycoengineering has had limited use in this field, due to the complexities of the endogenous O-glycosylation pathway and the lack of an O-glycosylation consensus sequence. Here, we describe the development of a versatile on-demand O-glycosylation system that uses a novel, widely applicable 5 amino acid O-glycosylation tag, and a metabolically engineered UDP-galactose-4-eperimase (GALE) knock-out cell line. Optimization of the primary sequence of the tag enables the production of Fc-based proteins with either single or multiple O-glycans with complexity fully controlled by media supplementation. We demonstrate how the uniformly labeled proteins containing exclusively N-azido-acetylgalactosamine are used for CLICK chemistry-based bioconjugation to generate site-specifically fluorochrome-labeled antibodies, dual-payload molecules, and bioactive Fc-peptides for applications in basic research and drug discovery. To our knowledge, this is the first description of generating a site-specific O-glycosylation system by combining an O-glycosylation tag and a metabolically engineered cell line.

Assessing the Extended In-Use Stability of the Infliximab Biosimilar PF-06438179/GP1111 Following Preparation for Intravenous Infusion.

OBJECTIVE: PF-06438179/GP1111 (PF-SZ-IFX) is an infliximab biosimilar. We evaluated the extended in-use physicochemical and biological stability of PF-SZ-IFX upon preparation for intravenous infusion. METHODS: Two batches of PF-SZ-IFX were reconstituted to a concentration of 10 mg/mL and subsequently diluted to 0.4 and 4.0 mg/mL, representing the clinically relevant range for intravenous infusion. Dilution was performed in polyethylene saline infusion bags, which are commonly used in clinical practice. To simulate product handling under worst-case conditions, reconstituted solutions were stored for up to 30 days at 5 ± 3 °C and up to 14 days at 25 ± 2 °C (60 ± 5% relative humidity); diluted solutions were stored for up to 30 days under the same sets of conditions. Physicochemical and biological stability were evaluated according to pH, osmolality, appearance, particulate content, protein concentration, proportions of molecular weight variants and charge variants and potency. Standard and state-of-the-art analytical techniques were employed, including imaged isoelectric focusing, size exclusion chromatography, reducing sodium dodecyl sulphate capillary electrophoresis and functional cell-based bioassay. RESULTS: Across batches and concentrations of PF-SZ-IFX, all parameters resided within the predefined acceptance criteria, including pH, osmolality, particulate content, clarity, protein concentration, molecular weight variants, charge variants and potency, for up to 30 days under both storage conditions tested (up to 14 days for reconstituted samples stored at 25 ± 2 °C). CONCLUSIONS: Physicochemical and biological analyses demonstrated that the infliximab biosimilar PF-SZ-IFX was not affected by extended storage of the diluted preparations used for intravenous infusion.

Engineering of a GLP-1 analogue peptide/anti-PCSK9 antibody fusion for type 2 diabetes treatment.

Type 2 diabetes (T2D) is a complex and progressive disease requiring polypharmacy to manage hyperglycaemia and cardiovascular risk factors. However, most patients do not achieve combined treatment goals. To address this therapeutic gap, we have developed MEDI4166, a novel glucagon-like peptide-1 (GLP-1) receptor agonist peptide fused to a proprotein convertase subtilisin/kexin type 9 (PCSK9) neutralising antibody that allows for glycaemic control and low-density lipoprotein cholesterol (LDL-C) lowering in a single molecule. The fusion has been engineered to deliver sustained peptide activity in vivo in combination with reduced potency, to manage GLP-1 driven adverse effects at high dose, and a favourable manufacturability profile. MEDI4166 showed robust and sustained LDL-C lowering in cynomolgus monkeys and exhibited the anticipated GLP-1 effects in T2D mouse models. We believe MEDI4166 is a novel molecule combining long acting agonist peptide and neutralising antibody activities to deliver a unique pharmacology profile for the management of T2D.

Dysregulation of the host mevalonate pathway during early bacterial infection activates human TCR gamma delta cells.

Primates, but not rodents, have T cell receptor Vgamma9-Vdelta2 T cells bridging innate and adaptive antimicrobial immunity. This T cell population is activated by prenyl pyrophosphates isolated from microbial or eukaryotic cells. Although the microbial metabolites are more active than the cellular ones, their involvement in TCR gammadelta activation during infection has not been studied. Here, we show that, during the initial phases of infections with Escherichia coli and Staphylococcus aureus, TCR gammadelta cells are activated by endogenous mevalonate metabolites. Infections with low bacteria inocula up-regulate the production and accumulation of host-derived TCR gammadelta stimulatory antigens within 1 h, which is followed by a peak of TCR gammadelta cell activation at 5 h. Infections induce the accumulation and dephosphorylation of the hydroxymethylglutaryl-coenzyme A reductase, the rate-limiting enzyme of the mevalonate pathway, resulting in increased activity of this enzyme and in increased synthesis of intermediate metabolites. Thus, primates have evolved the ability to readily respond to bacterial infection by sensing the dysregulation of the mevalonate pathway within infected cells, as a mechanism of immediate antimicrobial immunity.

Synthesis and biological evaluation of alpha-galactosylceramide (KRN7000) and isoglobotrihexosylceramide (iGb3).

Glycoceramides can activate NKT cells by binding with CD1d to produce IFN-gamma, IL-4, and other cytokines. An efficient synthetic pathway for alpha-galactosylceramide (KRN7000) was established by coupling a protected galactose donor to a properly protected ceramide. During the investigation, it was discovered that when the ceramide was protected with benzyl groups, only beta-galactosylceramide was produced from the glycosylation reaction. In contrast, the ceramide with benzoyl protecting groups produced alpha-galactosylceramide. Isoglobotrihexosylceramide (iGb3) was prepared by glycosylation of Galalpha1-3Galbeta1-4Glc donor with 2-azido-sphingosine in high yield. Biological assays on the synthetic KRN7000 and iGb3 were performed using human and murine iNKT cell clones or hybridomas.

Bacterial infections promote T cell recognition of self-glycolipids.

Recognition of self is essential for repertoire selection, immune regulation, and autoimmunity and may be a consequence of infection. Self-induced recognition may represent the escape mechanism adopted by pathogens but may also incite autoimmune diseases. Here, we show that bacterial infection may promote activation of T cells reactive to self-glycosphingolipids (self-GSL). CD1+ antigen-presenting cells (APCs) infected with bacteria (Escherichia coli, Bacillus subtilis, Staphylococcus aureus, or Mycobacterium bovis-Bacillus Calmette Guerín [BCG]) or treated with the bacterial components lipopolysaccharide, lipoteichoic acid, or Pam3CysSerLys4 (P3CSK4) lipopeptide acquire the capacity to stimulate self-GSL-specific T cells to cytokine release. Immediately after infection, APCs increase the endogenous GSL synthesis and stimulate GSL-specific T cells in a CD1- and T cell receptor (TCR)-dependent manner. This stimulation may contribute to inflammatory responses during bacterial infections and may predispose individuals to autoimmune diseases.

Ligands for natural killer cell-activating receptors are expressed upon the maturation of normal myelomonocytic cells but at low levels in acute myeloid leukemias.

Natural killer (NK) cell-mediated cytolytic activity against tumors requires the engagement of activating NK receptors by the tumor-associated ligands. Here, we have studied the role of NKG2D and natural cytotoxicity receptors (NCRs) in the recognition of human leukemia. To detect as-yet-unknown cell-surface molecules recognized by NCRs, we developed soluble forms of NKp30, NKp44, and NKp46 as staining reagents binding the putative cognate ligands. Analysis of UL16-binding protein-1 (ULBP1), ULBP2, and ULBP3 ligands for NKG2D and of potential ligands for NKp30, NKp44, and NKp46 in healthy hematopoietic cells demonstrated the ligand-negative phenotype of bone marrow-derived CD34(+) progenitor cells and the acquisition of cell-surface ligands during the course of myeloid differentiation. In acute myeloid leukemia (AML), leukemic blasts from approximately 80% of patients expressed very low levels of ULBPs and NCR-specific ligands. Treatment with differentiation-promoting myeloid growth factors, together with interferon-gamma, upregulated cell-surface levels of ULBP1 and putative NCR ligands on AML blasts, conferring an increased sensitivity to NK cell-mediated lysis. We conclude that the ligand-negative/low phenotype in AML is a consequence of cell maturation arrest on malignant transformation and that defective expression of ligands for the activating NKG2D and NCR receptors may compromise leukemia recognition by NK cells.

Is the cytoplasmic loop of MerT, the mercuric ion transport protein, involved in mercury transfer to the mercuric reductase?

In MerT, the mercury transporter, a first cysteine pair, located in the first trans-membrane helix, receives mercury from the periplasm. Then, a second cysteine pair, housed in a cytoplasmic loop connecting the second and the third trans-membrane helices, is thought to transfer the metal to another cysteine pair located in the N-terminal extension of the mercuric reductase. We found that a 23-amino acid synthetic peptide corresponding to the cytoplasmic loop can bind one mercury atom per molecule and that this mercury atom can be transferred specifically to MerAa. The solution structure of Hg-bound ppMerT has been solved by 1H NMR spectroscopy.

Crystal structure of the oxidized form of the periplasmic mercury-binding protein MerP from Ralstonia metallidurans CH34.

In Ralstonia metallidurans CH34, the gene merP encodes for a periplasmic mercury-binding protein which is capable of binding one mercury atom. The metal-binding site of MerP consists of the highly conserved sequence GMTCXXC found in the family that includes metallochaperones and metal-transporting ATPases. We purified MerP from R.metallidurans CH34 and solved its crystal structure under the oxidized form at 2.0A resolution. Superposition with structures of other metal-binding proteins shows that the global structure of R.metallidurans CH34 oxidized MerP follows the general topology of the whole family. The largest differences are observed with the NMR structure of oxidized Shigella flexneri MerP. Detailed analysis of the metal-binding site suggests a direct role for Y66 in stabilizing the thiolate group of C17 during the mercury-binding reaction. The metal-binding site of oxidized MerP is also similar to the metal-binding sites of oxidized copper chaperone for superoxide dismutase and Atx1, two copper-binding proteins from Saccharomyces cerevisiae. Finally, the packing of the MerP crystals suggests that F38, a well-conserved residue in the MerP family may be important in mercury binding and transfer. We propose a possible mechanism of mercury transfer between two CXXC motifs based on a transient bi-coordinated mercury intermediate.

Biophysical characterization of the MerP-like amino-terminal extension of the mercuric reductase from Ralstonia metallidurans CH34.

The purified native mercuric reductase (MerA) from Ralstonia metallidurans CH34 contains an N-terminal sequence of 68 amino acids predicted to be homologous to MerP, the periplasmic mercury-binding protein. This MerP-like protein has now been expressed independently. The protein was named MerAa by homology with Ccc2a, the first soluble domain of the copper-transporting ATPase from yeast. Deltaa has been characterized using a set of biophysical techniques. The binding of mercury was followed using circular dichroism spectroscopy and electrospray mass spectrometry. The two cysteine residues contained in the consensus sequence GMTC XXC are involved in the binding of one mercury atom, with an apparent affinity comparable to that of MerP for the same metal. The metal-binding site is confirmed by NMR chemical shift changes observed between apo- and metal-bound MerAa in solution. NMR shift and NOE data also indicate that only minor structural changes occur upon metal binding. Further NMR investigation of the fold of MerAa using long-range methyl-methyl NOE and backbone residual dipolar coupling data confirm the expected close structural homology with MerP. (15)N relaxation data show that MerAa is a globally rigid molecule. An increased backbone mobility was observed for the loop region connecting the first beta-strand and the first alpha-helix and comprising the metal-binding domain. Although significantly reduced, this loop region keeps some conformational flexibility upon metal binding. Altogether, our data suggest a role of MerAa in mercury trafficking.

Optimized set of two-dimensional experiments for fast sequential assignment, secondary structure determination, and backbone fold validation of 13C/15N-labelled proteins.

NMR experiments are presented which allow backbone resonance assignment, secondary structure identification, and in favorable cases also molecular fold topology determination from a series of two-dimensional 1H-15N HSQC-like spectra. The 1H-15N correlation peaks are frequency shifted by an amount +/- omegaX along the 15N dimension, where omegaX is the Calpha, Cbeta, or Halpha frequency of the same or the preceding residue. Because of the low dimensionality (2D) of the experiments, high-resolution spectra are obtained in a short overall experimental time. The whole series of seven experiments can be performed in typically less than one day. This approach significantly reduces experimental time when compared to the standard 3D-based methods. The here presented methodology is thus especially appealing in the context of high-throughput NMR studies of protein structure, dynamics or molecular interfaces.