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R Axel

Publications and source records attributed to R Axel.

At least 19 recordsLinked to original sources
PubMed1992

Alternative splicing generates functionally distinct N-methyl-D-aspartate receptors.

We have used expression cloning in Xenopus oocytes to isolate two different cDNAs encoding functional N-methyl-D-aspartate (NMDA) receptor subunits. The two receptors (NMDA-R1A and -R1B) display different pharmacologic properties as a consequence of alternative exon addition within the putative ligand-binding domain. The splicing choice is regulated such that R1B is the predominant form of receptor in the cerebellum, whereas R1A predominates in other brain regions. Expression of either of the subunits alone in oocytes results in an NMDA-evoked inward current with electrophysiologic properties closely resembling those of the NMDA receptors observed in neurons. Thus, the complex properties exhibited by the NMDA receptor in neurons can be generated by the expression of a single receptor subunit.

Amino Acid Sequence↗
PubMed1992

The level of CD8 expression can determine the outcome of thymic selection.

During thymic development, thymocytes that can recognize major histocompatability complex (MHC) molecules on thymic epithelial cells are selected to survive and mature (positive selection), whereas thymocytes that recognize MHC on hematopoietic cells are destroyed (negative selection). It is not known how MHC recognition can mediate both death and survival. One model to explain this paradox proposes that thymocytes whose T cell antigen receptors (TCRs) recognize MHC with high affinity are eliminated by negative selection, whereas low affinity TCR-MHC interactions are sufficient to mediate positive selection. Here we report that, while the expression of a 2C TCR transgene leads to positive selection of thymocytes in H-2b mice, expression of both a CD8 transgene and a 2C TCR transgene causes negative selection. This observation indicates that quantitative differences in TCR-MHC recognition are a critical determinant of T cell fate, a finding predicted by the affinity model for thymic selection.

Animals↗
PubMed1992

Crystal structure of a soluble form of the human T cell coreceptor CD8 at 2.6 A resolution.

A secreted fragment of the extracellular portion of human CD8 alpha has been expressed in CHO cells, and a deglycosylated and proteolyzed form of this fragment has been crystallized. We report here the crystal structure of this fragment as refined at 2.6 A resolution. The structure was solved by molecular replacement using a superposition of ten variable domains from immunoglobulin light chains as the search model. Only the N-terminal 114 amino acids of CD8 alpha are visible in the electron density maps. The domain formed by these residues possesses a fold typical of immunoglobulin variable domains and associates to form Fv-like homodimers.

Amino Acid Sequence↗
PubMed1992

Molecular cloning and single-channel properties of the cyclic nucleotide-gated channel from catfish olfactory neurons.

We have cloned a functional cDNA encoding the cyclic nucleotide-gated channel selectively expressed in catfish olfactory sensory neurons. The cyclic nucleotide-gated channels share sequence and structural features with the family of voltage-gated ion channels. This homology is most evident in transmembrane region S4, the putative voltage sensor domain, and the H5 domain, thought to form the channel pore. We have characterized the single-channel properties of the cloned catfish channel and compared these properties with the channel in native catfish olfactory sensory neurons. The channel is activated equally well by cAMP and cGMP, shows only a slight voltage dependence of gating, and exhibits a pH- and voltage-dependent subconductance state similar to that observed for the voltage-gated L-type calcium channel.

Amino Acid Sequence↗
PubMed1992

A self-reactive T cell population that is not subject to negative selection.

In male mice expressing a transgenic alpha beta TCR which recognizes a male antigen (HY), T cells which do not express normal levels of CD8 escape thymic deletion and appear in the periphery. These consist of two distinct populations, one which lacks expression of both CD4 and CD8, and one with low levels of CD8. Neither population has anti-HY reactivity, consistent with the known requirement of this TCR for CD8. We now describe the consequences of expression of both the anti-HY TCR transgene and a constitutive CD8.1 transgene on T cells of male mice. Peripheral T cells in these male 'double transgenic' mice express both the anti-HY TCR and normal levels of CD8, and can proliferate to male antigen in vitro. These cells do not express the endogenous allele of CD8 (CD8.2), suggesting that the increase in CD8 levels due to the CD8.1 transgene leads to the deletion of the CD8.2low population. In contrast, the CD8.1 transgene does not lead to the deletion of the CD8.2- population. This implies that, unlike the majority of alpha beta T cells, TCR+CD4-CD8- cells in TCR transgenic mice are not subject to deletion.

Animals↗
PubMed1991

Prohormone processing in Xenopus oocytes: characterization of cleavage signals and cleavage enzymes.

In this study, we characterize the sequences required for the cleavage of prohormones in Xenopus oocytes. We demonstrate that the yeast alpha-factor and the Aplysia egg-laying hormone (ELH) precursors are not cleaved in oocytes following simple pairs of basic residues, such as Lys-Arg, but that the ELH precursor is cleaved following the consensus sequence Arg-Xaa-(Lys/Arg)-Arg. This motif is conserved among precursors that are cleaved in virtually all mammalian cell types. Mutations that generate this sequence in the alpha-factor prohormone also result in efficient processing within oocytes. Cleavage at this consensus sequence may be due to the action of the Xenopus homologues of mammalian furin.

Amino Acid Sequence↗
PubMed1991

Isolation and functional expression of a mammalian prohormone processing enzyme, murine prohormone convertase 1.

We have combined gene cloning with an assay for prohormone biosynthesis and processing in Xenopus oocytes to identify the genes that encode mammalian prohormone processing enzymes. The coinjection of RNA encoding murine prohormone convertase 1 (mPC1), a mammalian endoprotease, along with proopiomelanocortin RNA into an oocyte results in the appropriate cleavage after paired basic residues in the proopiomelanocortin polyprotein necessary to generate corticotropin. The ability of mPC1 to generate corticotropin, along with the observation that mPC1 is specifically expressed in endocrine and neuronal cells, suggests that the mPC1 gene encodes the endopeptidase responsible for the pathway of proopiomelanocortin cleavage observed in the anterior pituitary.

Amino Acid Sequence↗
PubMed1991

A novel multigene family may encode odorant receptors: a molecular basis for odor recognition.

The mammalian olfactory system can recognize and discriminate a large number of different odorant molecules. The detection of chemically distinct odorants presumably results from the association of odorous ligands with specific receptors on olfactory sensory neurons. To address the problem of olfactory perception at a molecular level, we have cloned and characterized 18 different members of an extremely large multigene family that encodes seven transmembrane domain proteins whose expression is restricted to the olfactory epithelium. The members of this novel gene family are likely to encode a diverse family of odorant receptors.

Amino Acid Sequence↗
PubMed1991

Expression of CD4 in transgenic mice alters the specificity of CD8 cells for allogeneic major histocompatibility complex.

We have generated a transgenic mouse line in which a CD4 transgene is expressed on a significant fraction of the mature CD8+ lymphocytes but is not expressed in the thymus. This provides an opportunity to examine the functional consequences of CD4 expression in a population of class I-selected CD8+ lymphocytes. CD8+ lymphocytes expressing the CD4 transgene proliferate in response to allogeneic class I and class II major histocompatibility complex, whereas CD8+ cells from control animals proliferate only to allogeneic class I gene products. These observations suggest that the ability of a T-cell population to react with class II allogeneic major histocompatibility complex is determined by the presence of CD4.

Animals↗
PubMed1991

Thymic selection in CD8 transgenic mice supports an instructive model for commitment to a CD4 or CD8 lineage.

Immature thymocytes, which coexpress CD4 and CD8, give rise to mature CD4+CD8- and CD4-CD8+ T cells. Only those T cells that recognize self-MHC are selected to mature, a process known as positive selection. The specificity of the T cell antigen receptor (TCR) for class I or class II MHC influences the commitment to a CD4 or CD8 lineage. This may occur by a directed mechanism or by stochastic commitment followed by a selection step that allows only CD8+, class I-specific and CD4+, class II-specific cells to survive. We have generated a mouse line expressing a CD8 transgene under the control of the T cell-specific CD2 regulatory sequences. Although constitutive CD8 expression does not affect thymic selection of CD4+ cells, selection of a class I-specific TCR in the CD8 subset is substantially improved. This outcome is consistent with a model for positive selection in which selection occurs at a developmental stage in which both CD4 and CD8 are expressed, and positive selection by class I MHC generates an instructive signal that directs differentiation to a CD8 lineage.

Animals↗
PubMed1990

Crystal structure of an HIV-binding recombinant fragment of human CD4.

CD4 glycoprotein on the surface of T cells helps in the immune response and is the receptor for HIV infection. The structure of a soluble fragment of CD4 determined at 2.3 A resolution reveals that the molecule has two intimately associated immunoglobulin-like domains. Residues implicated in HIV recognition by analysis of mutants and antibody binding are salient features in domain D1. Domain D2 is distinguished by a variation on the beta-strand topologies of antibody domains and by an intra-sheet disulphide bridge.

Amino Acid Sequence↗
PubMed1990

Chromosome localization of human ARH genes, a ras-related gene family.

The human ARH genes (previously called RHO) share several properties with the ras gene family. Three members of the ARH family, the H6, H9, and H12 genes, have been localized to human chromosomes 2, 5, and 3, respectively. Analysis of DNAs from a rodent-human somatic cell hybrid panel demonstrates linkage of H6 to chromosome region 2p12----2pter and H9 to region 5q33----5qter. In situ chromosome hybridization also showed that the primary site for H9 is in the 5q31----qter region. The H12 gene was some-what difficult to localize using rodent-human hybrids because the probe detects a family of rodent genes as homologous to the human probe as in the human cognate gene. However, chromosome in situ hybridization revealed grains clustered in region 3p14----3p22 with a significant peak in band 3p21. We conclude that H6 is in 2p12----pter, H9 in 5q31----5qter, and H12 in 3p21.

Animals↗
PubMed1990

A family of glutamate receptor genes: evidence for the formation of heteromultimeric receptors with distinct channel properties.

We have isolated two cDNA clones (GluR-K2 and GluR-K3) that share considerable sequence identity with the previously described glutamate receptor subunit, GluR-K1. The three glutamate receptor subunits show significant sequence conservation with the glutamine binding component of the glutamine permease of E. coli. Each of these clones encodes a channel responsive to both kainate and AMPA. The coexpression of GluR-K2 with either GluR-K3 or GluR-K1 results in the formation of channels whose current-voltage relationships differ from those of the individual subunits alone and more closely approximate the properties of kainate receptors in neurons. These observations indicate that the kainate/quisqualate receptors are encoded by a family of genes and are likely to be composed of hetero-oligomers of at least two distinct subunits.

Amino Acid Transport Systems, Basic↗
PubMed1990

Molecular characteristics of recombinant human CD4 as deduced from polymorphic crystals.

We have grown crystals of a soluble recombinant form of human CD4, a transmembrane glycoprotein found predominantly on the surface of helper T cells. Crystals composed of the entire extracellular portion of CD4 exhibit extensive polymorphism. Of the five crystal types that have been grown, the best diffracts to Bragg spacings of 4.9 A. Symmetry considerations and characterization of the asymmetric unit by volume-specific amino acid analysis lead to the suggestion that a tetramer is the fundamental unit of crystallization. The characterization also showed that several of the crystal types have unusually high solvent contents. Because high solvent content and weak diffraction are indicative of an extended flexible structure, we examined the molecular shape of the recombinant CD4 with ultracentrifugation and found that it has an axial ratio of roughly 6, when modeled as a prolate ellipsoid. These results, combined with crystal packing constraints, suggest dimensions of approximately 25 x 25 x 125 A for a monomer. The structural features deduced here may be relevant to the biological function of CD4 as a receptor mediating cell-cell and cell-virus interactions.

Amino Acids↗
PubMed1990

The 5HT2 receptor defines a family of structurally distinct but functionally conserved serotonin receptors.

Serotonin exerts its diverse physiological effects by interacting with multiple distinct receptor subtypes. We have isolated a rat brain 5HT2 serotonin receptor cDNA by virtue of its homology with the 5HT1c receptor. The 5HT2 receptor is a member of the family of receptors that are linked to guanine nucleotide-binding proteins and are predicted to span the lipid bilayer seven times. Overall sequence identity between the 5HT2 and 5HT1c receptors is 49%, but identity within the transmembrane domains is 80%. Expression of both the 5HT2 and 5HT1c receptors in transfected mouse fibroblasts activates phospholipase C signaling pathways and promotes cellular transformation. However, RNA blotting shows that these two receptor subtypes are differentially expressed in the central nervous system. In this manner, structurally and functionally homologous receptor subtypes may elicit distinct physiologic actions.

Amino Acid Sequence↗