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M Sharon

Publications and source records attributed to M Sharon.

At least 19 recordsLinked to original sources
PubMed1999

2D-NMR and ATR-FTIR study of the structure of a cell-selective diastereomer of melittin and its orientation in phospholipids.

Melittin, a 26 residue, non-cell-selective cytolytic peptide, is the major component of the venom of the honey bee Apis mellifera. In a previous study, a diastereomer ([D]-V(5,8),I(17),K(21)-melittin, D-amino acids at positions V(5,8),I(17),K(21)) of melittin was synthesized and its function was investigated [Oren, Z., and Shai, Y. (1997) Biochemistry 36, 1826-1835]. [D]-V(5,8),I(17),K(21)-melittin lost its cytotoxic effects on mammalian cells; however, it retained antibacterial activity. Furthermore, [D]-V(5,8),I(17),K(21)-melittin binds strongly and destabilizes only negatively charged phospholipid vesicles, in contrast to native melittin, which binds strongly also zwitterionic phospholipids. To understand the differences in the properties of melittin and its diastereomer, 2D-NMR experiments were carried out with [D]-V(5,8),I(17),K(21)-melittin, and polarized attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy experiments were done with both melittin and [D]-V(5,8), I(17),K(21)-melittin. The structure of the diastereomer was characterized by NMR in water, as well as in three different membrane-mimicking environment, 40% 2,2,2-trifluoroethanol (TFE)/water, methanol, and dodecylphosphocholine/phosphatidylglycerol (DPC/DMPG) micelles. The NMR data revealed an amphipathic alpha-helix only in the C-terminal region of the diastereomer in TFE/water and methanol solutions and in DPC/DMPG micelles. ATR-FTIR experiments revealed that melittin and [D]-V(5,8),I(17),K(21)-melittin are oriented parallel to the membrane surface. This study indicates the role of secondary structure formation in selective cytolytic activity of [D]-V(5,8), I(17),K(21)-melittin. While the N-terminal helical structure is not required for the cytolytic activity toward negatively charged membranes and bacterial cells, it appears to be a crucial structural element for binding and insertion into zwitterionic membranes and for hemolytic activity.

Amino Acid Sequence↗
PubMed1992

Interleukin (IL)-2 and IL-3 induce distinct but overlapping responses in murine IL-3-dependent 32D cells transduced with human IL-2 receptor beta chain: involvement of tyrosine kinase(s) other than p56lck.

We have established IL-3-dependent 32D myeloid progenitor cells stably expressing the human IL-2 receptor beta chain (IL-2R beta). Whereas parental 32D cells proliferated only in response to IL-3, the transduced cells also proliferated in response to IL-2. Transduced cells expressed high- and intermediate-affinity IL-2Rs, resulting from expression of human IL-2R beta and murine IL-2R alpha chain (IL-2R alpha). IL-2 induced phenotypic changes not induced by IL-3, including the upregulated expression of endogenous murine IL-2R alpha and IL-2R beta and an increase in cell size. Therefore, the transduced IL-2R beta was not merely coupling with the IL-3 signaling pathway. IL-3 augmented several IL-2-induced responses including the up-regulation of IL-2R alpha. Both IL-2- and IL-3-induced proliferation and IL-2 induced IL-2R alpha expression were inhibited by the tyrosine kinase inhibitor herbimycin A. Thus, both IL-2- and IL-3-mediated effects required tyrosine kinase activity. The identity of the tyrosine kinase(s) mediating the IL-2 signals in these cells is not known but cannot be p56lck, a tyrosine kinase found in T cells, since 32D-IL-2R beta cells do not express p56lck.

Animals↗
PubMed1990

Structure, function, and regulation of the interleukin-2 receptor and identification of a novel immune activation gene.

This chapter is divided into two sections, the first dealing with a novel immune activation gene, denoted Act-2. This gene encodes a secreted protein that may represent a new cytokine. The Act-2 protein shares significant homology with proteins in two related families of small secreted proteins. Act-2 is rapidly synthesized by activated T cells, B cells and monocytes. The second section deals with interleukin-2 receptors. These receptors are now known to be comprised of three distinct classes of receptors, formed by various combinations of two IL-2 binding proteins, the alpha and beta chains. The low-affinity receptors contain alpha, but not beta chains; the intermediate-affinity receptors contain beta, but not alpha chains, and the high-affinity receptors contain both alpha and beta chains. The beta chain appears to be tyrosine phosphorylated. We discuss evidence for the existence of another protein of relative molecular mass 100,000, which appears to be a subunit of at least the high-affinity receptor.

Amino Acid Sequence↗
PubMed1990

A 100-kilodalton protein is associated with the murine interleukin 2 receptor: biochemical evidence that p100 is distinct from the alpha and beta chains.

Two proteins that specifically bind the T-cell growth factor interleukin 2 (IL-2) have been identified previously on the surface of T cells; these proteins have been designated IL-2R alpha and IL-2R beta for the alpha and beta chains of the IL-2 receptor (IL-2R). The association of these independent binding proteins with each other on the surface of activated T cells correlates with the generation of high-affinity binding sites. These high-affinity sites transduce the major mitogenic signal of IL-2, yet the mechanisms of association of the alpha and beta chains with each other as well as signal transduction in response to IL-2 are unknown. Cotransfection experiments of cDNAs encoding the alpha and beta chains in T cells and fibroblasts have suggested functional requirements for other T cell-specific factor(s). We now provide biochemical evidence for a distinct 100-kDa protein that interacts with the alpha or beta chains, or both, on the surface of the IL-2-dependent cell line CTLL-2 as well as activated murine splenocytes. This same 100-kDa protein is capable of being chemically cross-linked to 125I-labeled IL-2.

Animals↗
PubMed1990

Human interleukin 2 receptor beta-chain gene: chromosomal localization and identification of 5' regulatory sequences.

Interleukin 2 (IL-2) binds to and stimulates activated T cells through high-affinity IL-2 receptors (IL-2Rs). Such receptors represent a complex consisting of at least two proteins, the 55-kDa IL-2R alpha chain and the 70-kDa IL-2R beta chain. The low-affinity, IL-2R alpha chain cannot by itself transduce a mitogenic signal, whereas IL-2 stimulates resting lymphocytes through the intermediate-affinity, IL-2R beta receptor. We report here identification of the genomic locus for IL-2R beta. The exons are contained on four EcoRI fragments of 1.1, 9.2, 7.2, and 13.7 kilobases. The 1.1-kilobase EcoRI fragment lies at the 5'-most end of the genomic locus and contains promoter sequences. The promoter contains no TATA box-like elements but does contain the d(GT)n class of middle repetitive elements, which may play an interesting regulatory role. The IL-2R beta gene is localized to chromosome 22q11.2-q12, a region that is the locus for several lymphoid neoplasias.

Base Sequence↗
PubMed1989

The beta-chain of the IL-2 receptor (p70) is tyrosine-phosphorylated on YT and HUT-102B2 cells.

IL-2 has previously been shown to rapidly induce activity of a tyrosine kinase. High-affinity IL-2 receptors that mediate the major mitogenic signals of IL-2 contain both p70 and p55 chains. p55 has no potential tyrosine phosphorylation sites and lacks consensus sequences found in protein tyrosine kinases. Inasmuch as the phosphorylation of hormone receptors is generally an important mechanism for regulating receptor function, we have now investigated the phosphorylation status of p70. By using anti-phosphotyrosine antibodies to immunoprecipitate affinity-labeled IL-2 receptors and to probe Western blots, we provide data suggesting that p70, but not p55, is constitutively tyrosine-phosphorylated on the leukemic cell lines studied.

Cell Line, Transformed↗