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Myelin-associated glycoprotein (MAG) binds to the nerve cell surface and inhibits nerve regeneration. The nerve cell surface ligand(s) for MAG are not established, although sialic acid-bearing glycans have been implicated. We identify the nerve cell surface gangliosides GD1a and GT1b as specific functional ligands for MAG-mediated inhibition of neurite outgrowth from primary rat cerebellar granule neurons. MAG-mediated neurite outgrowth inhibition is attenuated by (i) neuraminidase treatment of the neurons; (ii) blocking neuronal ganglioside biosynthesis; (iii) genetically modifying the terminal structures of nerve cell surface gangliosides; and (iv) adding highly specific IgG-class antiganglioside mAbs. Furthermore, neurite outgrowth inhibition is mimicked by highly multivalent clustering of GD1a or GT1b by using precomplexed antiganglioside Abs. These data implicate the nerve cell surface gangliosides GD1a and GT1b as functional MAG ligands and suggest that the first step in MAG inhibition is multivalent ganglioside clustering.

Cubic cage compounds composed of Co-CN-Ru linkages have been prepared which illustrate the following features: (i) new motifs for alkali metal ion complexation (i.e., cationic receptors for cations), (ii) a new family of triaza-metalloligands, and (iii) a double box-like cage. The cages are synthesized by the condensation of [[CpCo[(CN).sub.3]].sup.-] and [[Cp*Ru[(NCMe).sub.3]].sup.+] (cyclopentadienyl, Cp; pentamethylcyclopentadienyl, Cp*) the presence of [Cs.sup.+]. The species [{Cs[subset]([[CpCo[(CN).sub.3]].sub.4][[Cp*Ru].sub.4]).sup.+] and {Cs[subset][{[[CpCo[(CN).sub.3]].sub.4][[Cp*Ru].sub.3][Cp*Rh]).sup.2+] illustrate the box-completion reaction Cs [subset] [Co.sub.4][Ru.sub.3] + M (M = Cp*[Rh.sup.2+], Cp*[Ru.sup.+]). With the naked ion precursors [[Na[(NCMe).sub.6]].sup.+] and [[Fe[(NCMe).sub.6]].sup.2+], the box-completion reactions afforded [{Na[{Cs[subset][[CpCo[(CN).sub.3]].sub.4][[Cp*Ru].sub.3]]}.sub.2]}.sup.+] and [{Fe[{Cs[subset] [[CpCo[(CN).sub.3]].sub.4][[Cp*Ru].sub.3]]}.sub.2]}.sup.2+]. These cages provide the first examples, to our knowledge, of the double-box motif.

Cellular immunity is mediated by the interaction of an [Alpha][Beta] T cell receptor (TCR) with a peptide presented within the context era major histocompatibility complex (MHC) molecule. Allereactive T cells have [Alpha][Beta] TCRs that can recognize both self- and foreign peptide - MHC (pMHC) complexes, implying that the TCR has significant complementarity with different pMHC. To characterize the molecular basis for alloreactive TCR recognition of pMHC, we have produced a soluble, recombinant form of an allereactive [Alpha][Beta] T cell receptor in Drosophila melanogaster cells. This recombinant TCR, 2C, is expressed as a correctly paired [Alpha][Beta] heterodimer, with the chains covalently connected via a disulfide bond in the C-terminal region. The native conformation of the 2C TCR was probed by surface plasmon resonance (SPR) analysis by using conformation-specific monoclonal antibodies, as well as syngeneic and allogeneic pMHC ligands. The 2C interaction with H-2[K.sub.b]-dEV8, H-2[K.sup.bm3]-dEV8, H-2[K.sup.b]-SIYR and H-2[L.sup.d]-p2Ca spans a range of affinities from [K.sub.d] = [10.sup.-4] to [10.sup.-6]M for the syngeneic (H-2[K.sup.b]) and allogeneic (H-2[K.sup.bm3], H-2[L.sup.d]) ligands. In general, the syngeneic ligands bind with weaker affinities than the allegeneic ligands, consistent with current threshold models of thymic selection and T cell activation. Crystallization of the 2C TCR required proteolytic trimming of the C-terminal residues of the [Alpha] and [Beta] chains. X-ray quality crystals of complexes or 2C with H-2[K.sup.b]-dEV8, H-2[K.sup.bm3]-dEV8 and H-2[K.sup.b]-SIYR have been grown.

Transporters such as ligand effect modulator-1 (LEM1) may selectively modulate the intracellular levels of steroid hormones. The differential functions of these transporters in mammalian cells may control hormone availability and consequently hormone signaling to specific cell types. Researchers isolated a yeast mutant, lem1, and cloned a wild-type LEM1 that could be a transport protein of the ATP-binding cassette family. Dexamethasone deposit is increased in lem1 cells, indicating that wild-type LEM1 decreases the strength of dexamethasone by exporting this ligand.

We propose a docking method that mimics the way proteins bind. The method accounts for the dominant driving forces at the different length scales of the protein binding process, allowing for an efficient selection of a downhill path on the evolving receptor-ligand-free energy landscape. Starting from encounter complexes with as much as 10 [Angstrom] rms deviation from the native conformation, the method locally samples the six dimensional space of rigid-body receptor-ligand structures subject to a van der Waals constraint. The sampling is initially biased only by the desolvation and electrostatic components of the free energy, which capture the partial affinity of unbound structures that are more than 4 [Angstrom] away from the native state. Below this threshold, improved discrimination is attained by adding an increasing fraction of the van der Waals energy to the force field. The method, with no free parameters, was tested in eight different sets of independently crystallized receptor-ligand structures consistently predicting bound conformations with the lowest free energies and appropriate stability gap around 2 [Angstrom] from the native complex. This multistage approach is consistent with the underlying kinetics and internal structure of the free energy funnel to the bound state. Implications for the nature of the protein binding pathways are also discussed.

The polytopic ligand 1 contains three different metal ion binding subunits forming two substructures that code for the self-assembly of two different coordination structures (helicate and grid type) under metal ion complexation. Reaction with Cu(II) and Zn(II) ions generates the coordinatively unsaturated architectures 8 and 9 resulting from the formation of two double helicate arrangements. Their crystal structure has been determined by x-ray diffraction. These results show that the double helical motif is expressed at the expense of the grid type one, indicating the dominant/recessive behavior of the system. Together with earlier studies on the linear combination and crossover processing schemes, the dominant/ recessive generation of 8 and 9 completes the demonstration of principle of the modes of multiple expression of molecular information in a multicode programmed chemical system.

Two distinct benzodiazepine binding sites have been identified, (i) a central site restricted to brain and (ii) a ubiquitously expressed mitochondrial binding site, the so-called peripheral-type benzodiazepine receptor (PBR). In this paper, we show that a benzazepine referred to as BBL22 (2-amino 9-chloro-7-(2-fluorophenyl)-5H -pyrimidol[5,4-d][2]benzazepine), which is classified as a PBR ligand based on structure, induces arrest in [G.sub.2]/M phase of the cell cycle in human tumor cell lines of both epithelial and hematopoietic cellular origin. After [G.sub.2]/M arrest, several tumor types, notably prostate and certain breast cancer lines exhibited significant apoptosis. Ideally, cancer therapies should selectively target tumor cells while sparing normal cell counterparts. BBL22 exhibited such selectivity, as it did not affect the growth and survival of nonmalignant breast and prostate epithelial lines. Moreover, BBL22 demonstrated structural requirements for this selective antitumor activity as 11 structurally related PBR ligands, including high-affinity ligands Ro5-4864 and PK11195, failed to induce tumor cell growth arrest or apoptosis. The in vivo antitumor activity of BBL22 was examined in a human xenograft model of androgen-independent prostate cancer where BBL22 significantly reduced the growth of PC3 prostate tumors without eliciting overt toxicity. Identification of BBL22 represents a tumor selective therapeutic strategy for a variety of human tumors.