Construction and Identification of New Molecular Markers of Triple-Negative Breast Cancer Stem Cells

Objective: We screened the TNBC stem cells using phage display (PD) and acquired the specific binding clones; and then the positive phage DNAs were amplified and extracted, synthesized with specific polypeptides, and labeled with fluorescein isothiocyanate (FITC). Finally, we identified the specificity of the polypeptides in vitro and in vivo.Methods: Human breast cancer cell line MDA-MB-231 and human mammary gland cell line hs578bst were chosen in our study, and MDA-MB-231 breast cancer stem cells (BCSCs) were cultured and identified by flow cytometry. The phage peptide library was screened using MDA-MB-231 BCSCs, the positive phage clones were identified by ELISA, and the DNA of the positive phages was extracted and sent to a biotechnology company for sequencing. According to the sequencing results, a specific polypeptide was synthesized and labeled with FITC. In the end, the specificity of a polypeptide to BCSCs was identified in vivo and in vitro.Results: The MDA-MB-231 BCSCs were cultured and enriched with the “serum and serum-free alternate” method. The BCSCs were found to have characteristics of CD44+/CD24−/low epithelial surface antigen (ESA) and ALDH+ with flow cytometry. The phage was enriched to 200-fold after three rounds of screening for MDA-MB-231 BCSCs. The positive phages were sequenced; then a polypeptide named M58 was synthesized according to sequencing results. Polypeptide M58 has a specific affinity to MDA-MB-231 BCSCs in vivo and in vitro.Conclusion: Specific polypeptides binding to MDA-MB-231 BCSCs were screened out by PD screening method, which laid a theoretical foundation for the targeted therapy and further research of BCSCs.

Identification of oligopeptides mimicking the receptor-binding domain of Hantaan virus envelope glycoprotein from a phage-displayed peptide library

Attachment of enveloped viruses to cells is triggered by the receptor-binding domain (RBD) on envelope glycoproteins (GP) binding to receptors located on the cell surface. To date, recognized receptors and RBD of hantaan virus (HTNV) have not been exactly defined. In this study, one monoclonal antibody (MAb) 3G1 possessing high neutralizing activity, which is directed against HTNV envelope glycoprotein G2, was used to determine the crucial motif of RBD. Peptide ligands binding to MAb 3G1 were selected from a 12 amino acid peptide library displayed on filamentous phages. After 3 rounds of selection, the binding capacity between phages and MAb 3G1 was examined byELISA. Afterwards the positive phage clones with high binding activity to MAb 3G1 were chosen and sequenced. The peptide sequences of positive phage clones were compared with that of HTNV 76–118 strain G2. A motif Y/F/WPW(X)HX1–2HY, aligned to the primary sequences of G2 96YPWHTAKCHY105, was identified from the peptide inserts in the 9 positive clones. Positive phages and synthesized peptide containing the motif were bound significantly to virus-susceptible cell (Vero-E6) membranes by ELISA and immunofluorescence assay, respectively. Therefore, the sequence on G2 between amino acid 96 and 105 may be a key motif of HTNV RBD recognized by viral receptors on target cell membranes. Further characterization of the motif would provide useful information in understanding of the cellular entry of HTNV.

Isolation of Peptide Ligands that Inhibit Glutamate Racemase Activity from a Random Phage Display Library

Several new antibacterial agents are currently being developed in response to the emergence of bacterial resistance to existing antibiotic substances. The new agents include compounds that interfere with bacterial membrane function. The peptidoglycan component of the bacterial cell wall is synthesized by glutamate racemase, and this enzyme is responsible for the biosynthesis of d-glutamate, which is an essential component of cell wall peptidoglycan. In this study, we screened a phage display library expressing random dodecapeptides on the surface of bacteriophage against an Escherichia coli glutamate racemase, and isolated specific peptide sequences that bind to the enzyme. Twenty-seven positive phage clones were analyzed, and seven different peptide sequences were obtained. Among them, the peptide sequence His-Pro-Trp-His-Lys-Lys-His-Pro-Asp-Arg-Lys-Thr was found most frequently, suggesting that this peptide might have the highest affinity to glutamate racemase. The positive phage clones and HPWHKKHPDRKT synthetic peptide were able to inhibit glutamate racemase activity in vitro, implying that our peptide inhibitors may be utilized for the molecular design of new potential antibacterial agents targeting cell wall synthesis.

SANITARY STUDIES ON MALTED MILK SHAKES1

Summary One hundred samples of vanilla flavored malted milk shakes were analyzed for the incidence of staphylococci and coliform organisms. Eighty-one samples contained coliform organisms and ten samples contained coagulase positive phage typable strains of staphylococci. A discussion of bacterial sanitary standards for products such as “malts” and “shakes” is presented.