Strong immunoreactivity of beta-amyloid precursor protein, including the beta-amyloid protein sequence, at human neuromuscular junctions.

At the postsynaptic domain of the human neuromuscular junction (NMJ), we have demonstrated strong concentrations of the N-terminus 45-62, C-terminus 676-695 and beta-amyloid protein sequences of beta-amyloid precursor protein (beta APP). We used well-characterized monoclonal and polyclonal antibodies for co-localization with three other postsynaptic proteins, applying double and triple fluorescence labeling. Strong immunoreactivity of all three beta APP sequences was found at all NMJs identified by bound alpha-bungarotoxin (alpha BT), where they co-localized with alpha BT and with immunoreactive desmin and dystrophin, which are postsynaptic proteins of human NMJs. This appears to be the first demonstration of beta APP sequences concentrated postsynaptically at human NMJs. beta APP may have a role in normal junction biology and possibly in some diseases affecting NMJs.     

The polymerase (L) protein of rinderpest virus interacts with the host cell protein striatin

Rinderpest virus (RPV) is a morbillivirus that causes a highly contagious disease affecting members of the order Artiodactyla. The viral L protein is the catalytic subunit of the RNA-dependent RNA polymerase. To search for host cell proteins with which L interacts, a library screen was performed using the yeast two-hybrid system. Several host cell proteins were recovered from the library screen as putative L-interactors; one of these was identified as striatin. A direct interaction between RPV L and striatin was confirmed using both co-immunoprecipitation assays and co-localisation studies using confocal microscopy. Striatin was also shown to co-localise with the RPV L protein in infected cells. The L proteins of morbilliviruses consist of three long highly conserved domains separated by short unconserved stretches of amino acids. The L domain with which striatin interacts was investigated by co-immunoprecipitation and striatin was shown to interact primarily with the central conserved domain.     

Expression and characterization of the human YWK-II gene, encoding a sperm membrane protein related to the alzheimer betaA4-amyloid precursorprotein

The YWK-II cDNA, RSD-2, encoding a sperm membrane protein was isolated from a rat testis cDNA expression library. Using the RSD-2 insert in combination with rapid amplification of cDNA ends (RACE), the corresponding human gene was isolated from a human testis cDNA expression library. The human testis cDNA, HSD-2, is 3654 bp in length and contains an open reading frame of 763 codons. Hydropathicity analysis showed that the deduced polypeptide is a single strand transmembrane protein. The deduced polypeptide has partial homology with the amyloid precursor protein (APP) and high homology with the amyloid precursor homologue, APLP2/APPH. The YWK-II gene was mapped and assigned to human chromosome locus: 11q24-25. Northern blotting of various human tissue RNAs using the HSD-2 cDNA as a probe showed that the gene is transcribed ubiquitously. The cytoplasmic domain of HSD-2 was expressed in Escherichia coli. In-vitro studies showed that the recombinant polypeptide bound to a GTP-binding protein (G(o)) and was phosphorylated by protein kinase C and cdc2 kinase. In mammalian F11 cells, the recombinant polypeptide was found to be coupled to G(o). Thus, the YWK-II component has the characteristics of a G(o)-coupled receptor and may be involved in G(o)-mediated signal transduction pathway. Protein kinase C and cdc2 kinase may regulate this pathway in spermatozoa by phosphorylating the cytoplasmic domain of the YWK-II component.     

ataxin-3相互作用蛋白的筛选及鉴定

目的 筛选ataxin-3的相互作用蛋白并进行互作结构域分析，探讨ataxin-3的功能和脊髓小脑型共济失调Ⅲ型／马查多-约瑟夫病的发病机理。方法应用酵母双杂交系统3，从成人脑eDNA文库中筛选和鉴定突变型ataxin-3的互作蛋白，构建ataxin-3蛋白羧基端Bait质粒，进行互作结构域分析。应用激光共聚焦显微镜观察ataxin-3与所筛到的互作蛋白在哺乳动物细胞中的共定位情况。结果分离获得5个新的ataxin-3互作蛋白，视紫红质-二磷酸鸟苷解离抑制因子α、苏素-1、氨氯吡嗪脒敏感性神经元阳离子通道2和2个未知新序列。结构域分析显示除1个未知蛋白与ataxin-3蛋白羧基端互作外，其余4个均与氨基端互作。在SH-SY5Y细胞的细胞核内，野生型ataxin-3与苏素-1共定位，突变型ataxin-3所形成的核内蛋白聚合体也与苏素-1共定位。结论 发现1个未知蛋白可能与ataxin-3蛋白羧基端互作，苏素1可能与ataxin-3蛋白氨基端互作，苏素化可能参与了ataxin-3蛋白的翻译后修饰和脊髓小脑型共济失调Ⅲ型/马查多-约瑟夫病的发病过程。     

Murine and human T11 (CD2) cDNA sequences suggest a common signal transduction mechanism

The murine equivalent of the cDNA encoding the human T11 (CD2) sheep erythrocyte-binding protein has been cloned. It codes for a putative transmembrane protein which is homologous to human T11. In contrast to immunoglobulins whose domains consist of anti-parallel beta sheets, we predict that mouse and human T11 external domains probably belong to the alpha/beta protein folding class. The cytoplasmic region of T11 is a lengthy, proline-rich segment; secondary structural analysis predicts it to have a nonglobular conformation. This elongated tail could allow for interaction with multiple other intracellular proteins and may contain a cation-binding site involved in T lineage activation.     

Molecular cloning of a cDNA encoding the human interleukin 4 receptor

Using the mouse interleukin 4 (IL-4) receptor cDNA as a probe, we isolated a cDNA encoding the human IL-4 receptor (hIL-4 receptor) from a multifactor-responsive human myeloid cell line, TF1. The cDNA encodes for an open reading frame of 825 amino acids including a signal sequence (25 amino acids), the external domain (207 amino acids), a transmembrane domain (24 amino acids), and a large cytoplasmic domain (569 amino acids). The human IL-4 receptor has a 65% identity with the mouse IL-4 receptor at the nucleic acid level and retains the typical structural motif of the previously described cytokine receptor family. COS7 cells transfected with the full-length cDNA expressed high levels (140,000 sites/cell) of IL-4 binding sites, with a Kd = 80 pM, an affinity identical to that of the original TF1 cells. Similar to IL-4 responsive cells, cross-linking of [125I]IL-4 to COS7 cells transfected with the cDNA showed a major protein of 130-150 kd and minor species of 55-85 kd.     

Cloning and identification of a novel ubiquitin-like protein,BMSC-UbP,from human bone marrow stromal cells

Ubiquitin is one of phylogenetically well-conserved proteins in all eukaryotes. Ubiquitin-dependent modification of protein contributes to fine regulation of cellular biological processes. Using large-scale screening of human bone marrow stromal cell (BMSC) cDNA library, we isolated a full-length cDNA of 1352 bp encoding 380 amino acids with a ubiquitin domain (UBQ), which was designed as bone marrow stromal cell-derived ubiquitin-like protein (BMSC-UbP). In addition to UBQ domain at its N-terminus, BMSC-UbP also possesses a ubiquitin-associated domain at its C-terminus, sharing moderate homology to some ubiquitin-like proteins such as UBIN, Chap1, and ubiquilin. BMSC-UbP localizes at chromosome 15q22.3-q23 as confirmed by blast search in human genome. BMSC-UbP mRNA is widely expressed in human multiple tissues and various tumor cell lines. Moreover, BMSC-UbP mRNA decreased in BMSC stimulated with PMA and increased in HL60 cells stimulated with LPS, suggesting that BMSC-UbP might play roles in regulation of BMSC function or cell differentiation through an evocator- and cell-specific pattern.     

Carboxyl-terminal fragments of beta-amyloid precursor protein bind to microtubules and the associated protein tau.

Alzheimer's disease is a neurodegenerative disorder characterized by protein depositions in intracellular and extracellular spaces in the brain. The intraneuronal deposits are formed by neurofibrillary tangles composed mainly of abnormally phosphorylated tau, a microtubule-associated protein, whereas the major constituent of the amyloid deposited extracellularly in the brain parenchyma and vessel walls is amyloid beta-protein (A beta). The proteolytic processing of the beta-amyloid precursor protein (beta PP) results in the generation of a complex set of carboxyl-terminal peptides that contain A beta. In this study, we have used fusion proteins containing carboxyl-terminal fragments of beta PP to investigate the association of beta PP with cellular components. We demonstrate that specific domains within the carboxyl end of beta PP contain binding sites for cytoskeletal components; one, within residues 1 to 28 of A beta, binds directly to tubulin, and the second one, within sequences carboxyl-terminal to A beta, binds tau and tubulin. We propose that the two neuropathological hallmarks of Alzheimer's disease, A beta deposition and neurofibrillary tangles, represent the residual of a disrupted beta PP-tubulin-tau complex.     

Interaction of hepatitis B virus core protein with human GIPC1

Up to now, little is known about hepatitis B virus core protein (HBc) interactions with host-cell proteins, although such interactions might be essential for virus propagation and pathogenicity. In this work, a human liver cDNA library was screened for proteins interacting with HBc. Among several HBc-interacting partners selected, it interacted most strongly with the human protein GIPC1. A common protein interaction domain, PDZ, was identified as the region that is sufficient for the interaction with HBc. The core protein has a putative C-terminal PDZ-interacting motif, and this sequence proved to be important for the interaction with GIPC1.     

Cloning and sequencing of the cDNA encoding the human homologue of the murine immunoglobulin-associated protein B29.

Membrane-bound immunoglobulins (Ig) on the surface of murine B cells are noncovalently associated with a heterodimeric protein complex of MB-1 and B29 (also called Ig-alpha and Ig-beta). The Ig-associated proteins are predicted to regulate the assembly and transport of the Ig complex to the cell surface and to couple membrane-bound Ig to intracellular signal transduction pathways. We have isolated and sequenced a full-length cDNA clone encoding the human homologue of the B29 protein. The predicted amino acid sequence was compared to its murine counterpart, to MB-1 and to the human T cell receptor (TcR)-associated CD3 proteins. The alignment of the human B29 protein with its murine counterpart revealed 90% homology in the C-terminal portion comprising the cytoplasmic tails, the transmembrane regions and the adjacent 26 amino acids of the extracellular regions. Only 59% homology was found in the rest of the Ig-like extracellular domains. The high degree of conservation observed for the C-terminal amino acids suggested that these domains of the proteins play important functional roles for the Ig complex. Indicative of this was the conservation of the antigen receptor tail motif D-(X)7-E/D-(X)2-Y-(X)2-L-(X)7-Y-(X)2-L/I which is thought to be a component of signal transduction pathways. This motif is also found in the human and murine MB-1 proteins as well as in the TcR-associated CD3 molecules. Further regions of homology between B29, MB-1 and the CD3 proteins included extracellular residues which were predicted to maintain the Ig-like structure, and hydrophilic residues within the transmembrane regions which may be utilized during the intracellular assembly and transport of the oligomeric Ig/MB-1/B29 or TcR/CD3 complexes. Thus the similarities found between B29, MB-1 and the CD3 proteins suggest conserved functions for both the Ig- and TcR-associated proteins.     

Identification of Entamoeba histolytica thiol-specific antioxidant as a GalNAc lectin-associated protein

Entamoeba histolytica is a human intestinal parasite that causes amebic dysentery. A cell surface amebic adhesin, the galactose and N-acetyl-D-galactosamine inhibitable (GalNAc) lectin mediates amebic adherence to and contact-dependent killing of host cells. Previous work has suggested that the GalNAc lectin transduces signals via protein interactions with its short cytoplasmic domain. We used a yeast two-hybrid system to screen an E. histolytica cDNA library for proteins that interact with the GalNAc lectin cytoplasmic domain. One isolate was the E. histolytica thiol-specific antioxidant (TSA). TSA is an enzyme that detoxifies hydrogen peroxide. TSA did not interact in yeast two-hybrid experiments with a mutant version of the lectin cytoplasmic domain, confirming the specificity of the lectin-TSA interaction. Furthermore, mutational analyses of the TSA isolate demonstrated that an in-frame five amino acid sequence introduced between amino acids 61-62 yielded a TSA mutant that did not interact with the lectin cytoplasmic domain upon expression in the yeast two-hybrid system. The association of TSA and GalNAc lectin was further supported by co-immunoaffinity purification. Confocal microscopy demonstrated co-localization of TSA and GalNAc lectin at sites of ameba:host cell contact. Recruitment of TSA by the GalNAc lectin suggests a novel mechanism of parasite defense against reactive oxygen intermediates generated by host peripheral mononuclear cells.     

Molecular characterisation and expression of CD4 in two distantly related marsupials: the gray short-tailed opossum (Monodelphis domestica) and tammar wallaby (Macropus eugenii)

The gene and corresponding cDNA for CD4 in the gray short-tailed opossum, Monodelphis domestica, and the cDNA sequence for CD4 in the tammar wallaby, Macropus eugenii, have been characterised. The opossum CD4 homolog reveals conserved synteny, preserved genomic organisation and analogous structural arrangement to human and mouse CD4. Opossum and tammar CD4 exhibit typical eutherian CD4 features including the highly conserved p56(lck) binding motif in the cytoplasmic region and the invariant cysteine residues in extracellular domains 1 and 4. Interestingly, the marsupial CD4 sequences substitute a tryptophan for the first cysteine in domain 2 negating the formation of a disulphide bond as seen in other eutherian CD4 sequences except human and mouse. Overall the marsupial CD4 sequences share amino acid identity of 59% to each other and 37-41% with eutherian mammals. However, in contrast to eutherian homologs, the marsupial CD4 sequences were found to be truncated at the terminal end of the cytoplasmic tail. This is the first report confirming the presence of CD4 in a marsupial and describing its key features.     

Regional distribution in human of a novel aortic collagen-associated microfibrillar protein.

We have reported two hypothetical proteins of human aorta, based on sequences cloned from a cDNA library constructed from mRNAs purified from the adventitia. These sequences have immunoglobulin-kappa (IgK)-like domains, and we have shown that microfibrils of the aortic adventia are immunoreactive with antibodies against IgK. The present study was performed to characterize more specifically the regional distribution in human of one of these proteins in particular and the distribution of matrix proteins with IgK-like motifs in general. An antibody was raised in rabbit against a synthetic peptide based on a unique sequence in one of the hypothetical proteins (NPSNRVTPQKNFP), which has not been reported in the sequence of any other known protein. This antibody and a rabbit anti-human IgK antibody were used as first antibodies in the staining reactions. A monoclonal mouse anti-smooth muscle cell alpha-actin antibody was also used. Immunoreactivity with the sequence-specific antibody was limited to the aorta and large vessels. Adventitial microfibrillar staining was more conspicuous in the abdominal aorta than in the thoracic aorta and in the internal iliac than in the external iliac artery. The immunoreactive protein was associated with fibroblasts and not smooth muscle cells. Immunoreactivity coated the collagen fibers diffusely, while elastin fibers were not stained. Further studies using antibodies against IgK demonstrated immunoreactivity of collagen and fibroblasts in a variety of tissues: spleen, ovary, testicle, cervix, prostate, skin, and breast (but not brain). Immunoglobulin motifs may be a feature of matrix proteins produced by fibroblasts in many tissues, but the first motif that we identified from a cDNA library of aortic adventitia appears to be specific to aorta and large vessels.