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5 recordsLinked to original sources
PubMed1992

Neuron-specific antigen HPC-1 from bovine brain reveals strong homology to epimorphin, an essential factor involved in epithelial morphogenesis: identification of a novel protein family.

We have already cloned the cDNA for the HPC-1 antigen, a neuron-specific protein antigen from the rat brain. Here we report the molecular cloning of the bovine HPC-1 antigen homologue, and much strong sequence conservation between rat and bovine. By searching the recent protein data base, it was found that the HPC-1 antigen revealed unusual similarity to epimorphin which was mesenchymal factor related to the morphogenesis of primitive epidermal tissues in embryonic stages. We also found that the HPC-1 antigen was identical to p35A (syntaxin) which bound both to a synaptic vesicle protein and to N-type calcium channel. Although the relationship of the physiological functions, structures and topologies along cellular membrane between the HPC-1 antigen and epimorphin have not been consistent yet, these two proteins belong to a novel protein family.

Amino Acid Sequence↗
PubMed2026

STX1B variant-specific synaptic dysfunction is associated with network hyperexcitability in human iPSC-derived neurons.

BACKGROUND: Variants in STX1B/syntaxin-1B are linked to a spectrum of fever-associated epilepsy syndromes. While studies in murine models have provided mechanistic insights, their relevance to human disease in a heterozygous context may be limited. METHODS: We investigated two pathogenic STX1B variants using isolated single neurons and neuronal network cultures derived from patient-specific induced pluripotent stem cells. These carried either a de novo p.G226R variant, associated with severe developmental epilepsy, or an InDel variant (p.K45delinsRCMIE/p.L46M) linked to a transient familial seizure syndrome. Synaptic function and network excitability were assessed using patch-clamp and multi-electrode array recordings, alongside morphological and transcriptomic profiling. FINDINGS: G226R exhibited both gain- and loss-of-function characteristics, with increased miniature excitatory postsynaptic current frequency in networks but not in autapses, and synaptic failure during sustained high-frequency stimulation. For the InDel variant, the predicted loss-of-function phenotype based on reduced syntaxin-1B levels was not detectable at the single-cell level, likely masked by compensatory synaptic upregulation. At the network level, however, both variants were associated with neuronal hyperexcitability, characterised by more frequent and prolonged bursting activity, with a much stronger phenotype in G226R-containing networks. Transcriptomic profiling revealed a differential dysregulation of synaptic and other neuronal genes. INTERPRETATION: The divergence between morphological, electrophysiological and transcriptomic findings suggests that compensatory mechanisms may contribute to network hyperexcitability. Initially engaged to maintain homoeostasis, they may ultimately contribute to a pathological network state. The graded severity of network alterations across STX1B variants correlates with the clinical phenotypes. FUNDING: BMBF (Treat ION-01GM2210A, SNAREopathies-01EW1809A), 2023 FEBS Summer Fellowship, Fortüne programme (2610-0-0), EKFS college precise.net, Open Access Publishing Fund of University of Tübingen.

Humans↗
PubMed1992

Syntaxin: a synaptic protein implicated in docking of synaptic vesicles at presynaptic active zones.

Synaptic vesicles store neurotransmitters that are released during calcium-regulated exocytosis. The specificity of neurotransmitter release requires the localization of both synaptic vesicles and calcium channels to the presynaptic active zone. Two 35-kilodalton proteins (p35 or syntaxins) were identified that interact with the synaptic vesicle protein p65 (synaptotagmin). The p35 proteins are expressed only in the nervous system, are 84 percent identical, include carboxyl-terminal membrane anchors, and are concentrated on the plasma membrane at synaptic sites. An antibody to p35 immunoprecipitated solubilized N-type calcium channels. The p35 proteins may function in docking synaptic vesicles near calcium channels at presynaptic active zones.

Amino Acid Sequence↗
PubMed1992

HPC-1 is associated with synaptotagmin and omega-conotoxin receptor.

Monoclonal antibodies were produced that recognize a membrane protein of 35,000 Da (p35) expressed in brain and adrenal medulla. They immunoprecipitated 50% of omega-conotoxin (omega-CgTX) receptor, a putative N-type calcium channel, solubilized from rat brain. Anti-synaptotagmin (p65) antibodies also immunoprecipitate omega-CgTX receptor (Leveque, C., Hoshino, T., David, P., Shoji-Kasai, Y., Leys, K., Omori, A., Lang, B., El Far, O., Sato, K., Martin-Moutot, N., Newsom-Davis, J., Takahashi, M., and Seagar, M.J. (1992) Proc. Natl. Acad. Sci. U. S. A. 89, 3625-3629); however, immunoprecipitation by anti-p35 antibodies and anti-synaptotagmin antibodies was not additive. Furthermore, both p35 and synaptotagmin were recovered in the immunoprecipitates with anti-synaptotagmin and anti-p35 antibodies, respectively, indicating that a population of omega-CgTX receptor exists as a ternary complex with synaptotagmin and p35. A cDNA coding p35 was isolated from a rat brain cDNA library by immuno-screening, and the primary structure of the protein was revealed to be identical to that of HPC-1 (Inoue, A., Obata, K., and Akagawa, K. (1992) J. Biol. Chem. 267, 10613-10619). HPC-1 has a putative transmembrane segment at the C terminus and four heptad motifs, which may be involved in protein-protein interaction. These results suggest that HPC-1 may play a role in neurotransmitter release from nerve terminals by associating with omega-CgTX-sensitive N-type calcium channel and synaptotagmin.

Amino Acid Sequence↗
PubMed1992

Cloning and sequence analysis of cDNA for a neuronal cell membrane antigen, HPC-1.

A monoclonal antibody (mAb), HPC-1, labels the plasma membrane of the amacrine cell soma and inner plexiform layer in rat retina and other central neurons. HPC-1 antigen recognizes several proteins of about 35 kDa. In this study, an HPC-1 positive cDNA, HPC-113, was isolated from a lambda gt11 cDNA library of the rat hippocampus. HPC-113 had the 894-base pair nucleotide sequence in an open reading frame and the calculated molecular mass of the deduced amino acid sequence (298 residues) was 33,989 Da, implying that HPC-113 contains almost the full-length coding region of HPC-1 antigen is an integrated membrane protein revealing the characteristic alpha-helical structure with periodical heptad repeats usually seen in proteins with coiled-coil structures. Although the entire amino acid sequence did not show significant homology to any proteins so far known, a few local sequences in the possible extracellular domain of the HPC-1 antigen molecule had notable homology to some partial sequences in the laminin B1 chain. These sequences of laminin are included in the portion which has neurite outgrowth and/or survival promoting activity. The HPC-1 gene was transcribed in nerve tissues much more predominantly than in non-neuronal tissues. Thus, HPC-1 antigen(s) was confined to be a newly identified neuronal cell membrane protein(s) localized in a subpopulation of neurons.

Amino Acid Sequence↗