Monitoring the Disulfide Bonds of Folding Isomers of Synthetic CTX A3 Polypeptide Using MS-Based Technology.

Native disulfide formation is crucial to the process of disulfide-rich protein folding in vitro. As such, analysis of the disulfide bonds can be used to track the process of the folding reaction; however, the diverse structural isomers interfere with characterization due to the non-native disulfide linkages. Previously, a mass spectrometry (MS) based platform coupled with peptide demethylation and an automatic disulfide bond searching engine demonstrated the potential to screen disulfide-linked peptides for the unambiguous assignment of paired cysteine residues of toxin components in cobra venom. The developed MS-based platform was evaluated to analyze the disulfide bonds of structural isomers during the folding reaction of synthetic cardiotoxin A3 polypeptide (syn-CTX A3), an important medical component in cobra venom. Through application of this work flow, a total of 13 disulfide-linked peptides were repeatedly identified across the folding reaction, and two of them were found to contain cysteine pairings, like those found in native CTX A3. Quantitative analysis of these disulfide-linked peptides showed the occurrence of a progressive disulfide rearrangement that generates a native disulfide bond pattern on syn-CTX A3 folded protein. The formation of these syn-CTX A3 folded protein reaches a steady level in the late stage of the folding reaction. Biophysical and cell-based assays showed that the collected syn-CTX A3 folded protein have a ß-sheet secondary structure and cytotoxic activity similar to that of native CTX A3. In addition, the immunization of the syn-CTX A3 folded proteins could induce neutralization antibodies against the cytotoxic activity of native CTX A3. In contrast, these structure activities were poorly observed in the other folded isomers with non-native disulfide bonds. The study highlights the ability of the developed MS platform to assay isomers with heterogeneous disulfide bonds, providing insight into the folding mechanism of the bioactive protein generation.

Thermal properties and physicochemical behavior in aqueous solution of pyrene-labeled poly(ethylene glycol)-polylactide conjugate.

A fluorescence-labeled bioresorbable polymer was prepared by a coupling reaction of poly(ethylene glycol)-polylactide (PEG-PLA) with carboxyl pyrene, using N,N'-diisopropylcarbodiimide/1-hydroxy-7-azabenzotriazole (DIC/HOAt) as a coupling agent and 4-dimethylaminopyridine (DMAP) as a catalyst. The obtained copolymer, termed PEG-PLA-pyrene, was characterized using various analytical techniques, such as gel permeation chromatography (GPC), matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), proton nuclear magnetic resonance ((1)H-NMR), infrared spectroscopy (IR), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA), to identify the molecular structure and to monitor the thermal property changes before and after the reaction. The presence of a pyrene moiety at the end of polylactide (PLA) did not alter the crystallization ability of the poly(ethylene glycol) (PEG) blocks, indicating that the conjugate preserved the inherent thermal properties of PEG-PLA. However, the presence of PEG-PLA blocks strongly reduced the melting of pyrene, indicating that the thermal characteristics were sensitive to PEG-PLA incorporation. Regarding the physicochemical behavior in aqueous solution, a higher concentration of PEG-PLA-pyrene resulted in a higher ultraviolet-visible (UV-vis) absorbance and fluorescence emission intensity. This is of great interest for the use of this conjugate as a fluorescence probe to study the in vivo distribution as well as the internalization and intracellular localization of polymeric micelles.

A novel emulsion-type adjuvant containing CpG oligodeoxynucleotides enhances CD8+ T-cell-mediated anti-tumor immunity.

PELC is a novel emulsion-type adjuvant that contains the bioresorbable polymer poly (ethylene glycol)-block-poly (lactide-co-ε-caprolactone) (PEG-b-PLACL), Span®85 and squalene. To investigate whether PELC is able to enhance CTL responses of antigens for treating tumor, peptides or protein antigens derived from HPV16 E7 were formulated with PELC nanoparticles and CpG oligodeoxynucleotide. We identified that PELC formulation could delay the release of antigens in vitro and in vivo. We assessed the immunogenicity of an H-2D(b)-restricted CTL epitope RAHYNIVTF (RAH) formulated with PELC or PELC/CpG and investigated the ability of these formulations to promote tumor regression. Following a single-dose subcutaneous injection in mice, we found that the RAH peptide formulated with PELC/CpG (RAH/PELC/CpG) resulted in increased numbers of IFN-γ-secreting cells and RAH-specific CD8(+) T cells and an enhanced cytotoxic T cell response compared with RAH formulated with PELC or CpG alone. The tumor-bearing mice received a single-dose injection of RAH/PELC/CpG, which induced complete tumor regression. These results demonstrated that peptide antigen formulated with PELC/CpG nanoparticles is feasible for cancer immunotherapy.

Enzymatic stability and immunoregulatory efficacy of a synthetic indolicidin analogue with regular enantiomeric sequence.

Cell-mediated immunity plays a major role in protecting the host from viral infections and tumor challenge. Here, we report the enzymatic stability and adjuvanticity of a peptiomimetic stereoisomer of the bovine neutrophil peptide indolicidin. The analogue, dubbed ld-indolicidin, contains the regular enantiomeric sequence of indolicidin and is synthesized by general stepwise solid-phase strategy. ld-Indolicidin possesses high resistance to enzymatic degradation and shows tolerance in mice. As vaccine adjuvant, ld-indolicidin is better able than the native form of indolicidin to enhance cell-mediated immune responses, using inactivated H5N1 virus as a model antigen. Taken together, these results open up a new approach to the development of vaccine adjuvants and immunotherapy technologies.

A novel HLA-A2-restricted CTL epitope of tumor-associated antigen L6 can inhibit tumor growth in vivo.

Vaccines utilizing cytotoxic T lymphocyte (CTL) epitopes are promising for the treatment of cancer and chronic infectious diseases. Tumor-associated antigen L6 (TAL6) is overexpressed in some epithelial cancer cells. In this report, we detected TAL6 expression in breast cancer tissue using quantitative reverse-transcriptase-polymerase chain reaction. We found that >80% of breast tumor tissue highly expressed TAL6 compared with adjacent normal breast tissue. To identify CTL epitopes from TAL6, we synthesized 18 peptides for HLA-A2-binding assay based on the MHC-binding motif using 4 computer prediction programs. Positive binders identified by ELISA were immunized in HLA-A2 transgenic (A2 Tg) mice. Two peptides, peptide 2 and peptide 5, induced T-cell responses in A2 Tg mice. To confirm whether these peptides could be processed and presented to induce T-cell responses in vivo, A2 Tg mice were immunized with plasmid DNA encoding TAL6. We found that both peptides 2 and 5 stimulated splenocytes from TAL6-immunized mice to secrete interferon-γ. However, only peptide 5 could induce expression of the cytolytic molecule CD107a on CD8+ T cells after immunization. Furthermore, peptide 5-immunized A2 Tg mice could inhibit the growth of TAL6-positive tumors (EL4/TAL6/HLA-A2) in A2 Tg mice but not in wild-type mice. These results demonstrate that the TAL6-derived CTL epitope could induce HLA-A2-restricted immunity against TAL6-expressing tumor cells.

Presentation of lipopeptide by dendritic cells induces anti-tumor responses via an endocytosis-independent pathway in vivo.

Cross-presentation by DCs is the major mechanism by which exogenous antigens activate CTLs. However, the mechanisms of entry and presentation of vaccine peptides by DCs remain unclear. In this study, we determined that the mechanisms of antigen presentation differed between nonlipidated and monopalmitoylated peptide antigens. We found that a nonlipidated long peptide could be taken up by DCs and that the peptide could be colocalized with early endosomes. The uptake of nonlipidated peptides by DCs was inhibited at low temperatures or by the depolymerization of actin filaments or microtubules. In contrast, lipidated peptides were internalized by DCs at low temperatures, and internalization was not inhibited when actin filaments or microtubules were depolymerized. Moreover, lipidated peptide, but not nonlipidated peptide, was internalized by nonphagocytic Jurkat cells. The endosomal/lysosomal and proteasomal degradation pathways were necessary for nonlipidated presentation leading to the activation of CD8(+) T cells, but the proteasomal degradation pathway alone was sufficient to process lipidated peptides for MHC class I presentation. We further found that lipidated peptides could enhance peptide-specific T cell responses in vitro and in vivo and induced stronger antitumor responses than nonlipidated peptides. Taken together, our results demonstrate that DCs present lipidated peptides through an endocytosis-independent pathway to promote strong anti-tumor effects in vivo.

Identification of HLA-A11-restricted CTL epitopes derived from HPV type 18 using DNA immunization.

Identification of the cytotoxic T lymphocyte (CTL) epitopes of tumor antigens is important for effective immunotherapy. We report that a combination of epitope prediction, enzyme-linked immunosorbent assay (ELISA)-based epitope-HLA complex formation, and DNA immunization methods can improve the efficiency and accuracy of CTL epitope studies. In this study, two HLA-A11-restricted epitopes derived from human papillomavirus (HPV)18 E6 oncoprotein were identified. HLA-A11-transgenic mice immunized with these epitopes could specifically induce interferon-gamma (IFNgamma) production, cytotoxicity and peptide/HLA-A11 tetramer binding in CD8(+) T-cells. To study intracellular processing of CTL epitopes, we constructed a DNA plasmid containing an endoplasmic reticulum (ER) targeting sequence as well as the HPV18 E6 and E7 genes (pEK/HPV18E6E7). CTL responses against peptide-pulsed T2/A11 cells could be detected after immunizing HLA-A11-transgenic mice with pEK/HPV18E6E7. Furthermore, the identified peptides could stimulate T-cells to secrete IFNgamma from HPV18-infected patients. Our results demonstrate that the antigenic E6 peptides derived from HPV18 are potential candidates for the treatment of HPV 18-associated tumors in HLA-A11(+) populations.

NMR solution structure of KP-TerB, a tellurite-resistance protein from Klebsiella pneumoniae.

Klebsiella pneumoniae (KP), a Gram-negative bacterium, is a common cause of hospital-acquired bacterial infections worldwide. Tellurium (Te) compounds, although relatively rare in the environment, have a long history as antimicrobial and therapeutic agents. In bacteria, tellurite (TeO(3) (-2)) resistance is conferred by the ter (Te(r)) operon (terZABCDEF). Here, on the basis of 2593 restraints derived from NMR analysis, we report the NMR structure of TerB protein (151 amino acids) of KP (KP-TerB), which is mainly composed of seven alpha-helices and a 3(10) helix, with helices II to V apparently forming a four-helix bundle. The ensemble of 20 NMR structures was well-defined, with a RMSD of 0.32 +/- 0.06 A for backbone atoms and 1.11 +/- 0.07 A for heavy atoms, respectively. A unique property of the KP-TerB structure is that the positively and negatively charged clusters are formed by the N-terminal positively and C-terminal negatively charged residues, respectively. To the best of our knowledge, the protein sequence and structures of KP-TerB are unique.

Crystallization and preliminary X-ray diffraction analysis of thermophilic imidase from pig liver.

Imidase is an enzyme, also known as dihydropyrimidinase (EC 3.5.2.2), hydantoinase, dihydropyrimidine hydrase or dihydropyrimidine amidohydrolase, that catalyzes the reversible hydrolysis of 5,6-dihydrouracil to 3-ureidopropionate and many other imides. Substrate specificity, metal content and amino-acid sequence all differ significantly between bacterial and mammalian imide-hydrolyzing enzymes. In this study, a thermophilic imidase was isolated from pig liver and crystallized. Two kinds of imidase crystals were grown by the hanging-drop vapour-diffusion method using polyethylene glycol MME 5000 and 2-propanol as precipitants. One belongs to the triclinic P(1) space group, with unit-cell parameters a = 96.35, b = 96.87, c = 154.87 A, alpha = 82.10, beta = 72.54, gamma = 77.19 degrees, and the other belongs to the orthorhombic C222(1) space group, with unit-cell parameters a = 113.92, b = 157.22, c = 156.21 A.