皖籍汉族正常人群TAP等位基因多态性分析

抗原处理相关转运蛋白体 (transporter associated with antigen processing, TAP)基因位于HLAⅡ类区域的DQB1和DPB1位点之间, 包括TAP1和TAP2,相距约70 kb.TAP基因产物是内质网膜上的跨膜二聚体,功能是将与胞浆内的蛋白酶体(proteosome)结合后并降解的内源性抗原转运至内质网腔,与HLAⅠ类分子结合,形成稳定的HLA-Ag复合物,然后才能表达于细胞表面并提呈给T细胞. Colonna M等[1]通过基因测序获得TAP全基因序列,证实该基因具有高度多态性和变异性.TAP的多态性可使不同的肽转运至内质网,因此,不同个体的MHCⅠ类分子对同一大分子提呈的抗原片段不同,从而使不同机体对同一抗原的免疫应答表现出个体差异[2].本研究对皖籍汉族正常人群进行TAP等位基因分型,并与不同种族、不同地区的资料进行比较,为进一步研究TAP关联疾病的发病机制奠定基础.     

抗原处理相关转运蛋白(TAP)的研究进展

抗原处理相关转运蛋白 (TAP)负责内源性抗原从胞浆到内质网的转运 ,在MHCⅠ类分子的抗原呈递过程中发挥重要的作用。TAP属于ABC超家族成员 ,其两个亚基共同参与组成肽结合部位 ,由于具有一定的多态性 ,对底物具有选择性转运现象。TAP同时还参与了MHCⅠ类分子的组装。体内外多种因素可以调节TAP的表达和活性 ,从而影响病毒感染过程和肿瘤的发生     

046 抗原处理相关转运蛋白(TAP)的研究进展

抗原处理相关转运蛋白(TAP)负责内源性抗原从胞浆到内质网的转运,在MHCⅠI类分子的抗原呈递过程中发挥重要的作用.TAP属于ABC超家族成员,其两个亚基共同参与组成肽结合部位,由于具有一定的多态性,对底物具有选择性转运现象.TAP同时还参与了MHC Ⅰ类分子的组装.体内外多种因素可以调节TAP的表达和活性,从而影响病毒感染过程和肿瘤的发生.     

抗原处理相关转动蛋白（TAP）的研究进展

抗原处理相关转运蛋白（TAP）负责内源性抗原从胞浆到内质网的转运，在MHCⅠ类分子的抗原呈递过程中发挥重要的作用。TAP属于ABC超家族成员，其两个亚基共同参与组成肽结合部位，由于具有一定的多态性，对底物具有选择性转运现象，TAP同时还参与了MHCⅠ类分子的组装。体内外多种因素可以调节TAP的表达和活性，从而影响病毒感染过程和肿瘤的发生。     

抗原提呈相关转运体基因多态性与慢性HBV感染研究进展

抗原提呈相关转运体（TAP）在内源性抗原提呈过程中有重要作用,负责内源性抗原从胞浆到内质网腔的转运。TAP是由TAP1基因和TAP2基因编码的TAP1和TAP2组成的异二聚体。TAP基因具有多态性。乙型肝炎病毒（HBV）作为细胞内抗原,主要是经过内源性抗原加工和提呈途径而启动免疫应答的,TAP1／TAP2基因多态性的改变造成了分子结构异常,则会出现抗原呈递的功能障碍,抗原提呈不能有效进行,HBV抗原肽不能被细胞毒细胞识别而清除,则形成HBV的慢性持续感染。     

人类TAP1基因克隆及表达载体的构建

抗原处理相关转运体(TAP)属于ABC(ATP-himding cassette)转运体超家族B亚家族。人类TAP基因位于6号染色体上的MHC-11类基因区．其编码的TAP1和TAP2分子．分别由748和686个氨基酸残基所组成，两者可形成异源二聚体参与肽类的转运过程．在MHC-I类分子介导的抗原递呈途径中起着重要作用^[1,2]。因此，TAP的异常将严重影响抗原     

抗原处理相关转运体结构与功能的研究进展

内源性抗原通过MHCⅠ类分子提呈给细胞毒性T细胞 (CTL)是机体细胞免疫识别的重要阶段。抗原处理相关转运体 (transporterassociatedwithantigenprocessing ,TAP)负责抗原肽从胞浆到内质网的转运 ,在MHCⅠ类分子的抗原处理及提呈过程中发挥重要作用。TAP结构和功能障碍将导致细胞表面MHCⅠ类分子表达缺陷 ,这成为肿瘤细胞、病毒感染细胞逃逸免疫监视的重要机制。     

057 抗原处理相关转运体结构与功能的研究进展

内源性抗原通过MHCⅠ类分子提呈给细胞毒性T细胞(CTL)是机体细胞免疫识别的重要阶段.抗原处理相关转运体(transporter associated with antigen processing,TAP)负责抗原肽从胞浆到内质网的转运,在MHCⅠ类分子的抗原处理及提呈过程中发挥重要作用.TAP结构和功能障碍将导致细胞表面MHC Ⅰ类分子表达缺陷,这成为肿瘤细胞、病毒感染细胞逃逸免疫监视的重要机制.     

抗原处理相关转运体结构与功能的研究进展

内源性抗原通过MHCⅠ类分子提呈给细胞毒性T细胞(CTL)是机体细胞免疫识别的重要阶段。抗原处理相关转运体(transporter associated with antigen processing,TAP)负责抗原肽从胞浆到内质网的转运，在MHCⅠ类分子的抗原处理及提呈过程中发挥重要作用。TAP结构和功能障碍将导致细胞表面MHCⅠ类分子表达缺陷，这成为肿瘤细胞、病毒感染细胞逃逸免疫监视的重要机制。     

宫颈病变中抗原呈递元件成员蛋白和人类白细胞共同抗原Ⅰ类分子表达的关系

抗原呈递元件(APM)成员蛋白作为一组抗原呈递相关功能蛋白,在协助人类白细胞共同抗原(HLA)Ⅰ类分子组装、负载和提呈内源性抗原肽,介导抗病毒T细胞免疫中发挥着重要作用[1].其成员蛋白抗原处理相关转运体(TAP)负责将内源性抗原肽向内质网腔转运.TAP相关蛋白对HLA-Ⅰ类分子在内质网中的装配发挥关键作用[2].分子伴侣钙连接蛋白和钙网蛋白以及疏基二硫键氧化还原酶Erp57协助新合成的HLA-Ⅰ蛋白正确折叠和组装[3].人乳头状瘤病毒(HPV)是宫颈癌发生的始动因素,也可能通过协助肿瘤细胞影响HLA-Ⅰ基因表达调控.因此,探讨HPV感染引起宿主HLA-Ⅰ类分子表达缺失与APM成员表达情况有无关联,是揭示肿瘤的分子机制、疫苗治疗、建立肿瘤生物标志谱体系的关键.我们通过检测宫颈上皮内瘤变(CIN)和宫颈癌组织中APM成员蛋白及HLA-Ⅰ类分子的表达情况,分析其与HPV16感染的相关性,从而探讨宫颈病变中HLA-Ⅰ类分子表达下调的机制.     

Intracellular peptide transporters in human – compartmentalization of the “peptidome”

In the human genome, the five adenosine triphosphate (ATP)-binding cassette (ABC) half transporters ABCB2 (TAP1), ABCB3 (TAP2), ABCB9 (TAP-like), and in part, also ABCB8 and ABCB10 are closely related with regard to their structural and functional properties. Although targeted to different cellular compartments such as the endoplasmic reticulum (ER), lysosomes, and mitochondria, they are involved in intracellular peptide trafficking across membranes. The transporter associated with antigen processing (TAP1 and TAP2) constitute a key machinery in the major histocompatibility complex (MHC) class I-mediated cellular immune defense against infected or malignantly transformed cells. TAP translocates the cellular "peptidome" derived primarily from cytosolic proteasomal degradation into the ER lumen for presentation by MHC class I molecules. The homodimeric ABCB9 (TAP-like) complex located in lysosomal compartments shares structural and functional similarities to TAP; however, its biological role seems to be different from the MHC I antigen processing. ABCB8 and ABCB10 are targeted to the inner mitochondrial membrane. MDL1, the yeast homologue of ABCB10, is involved in the export of peptides derived from proteolysis of inner-membrane proteins into the intermembrane space. As such peptides are presented as minor histocompatibility antigens on the surface of mammalian cells, a physiological role of ABCB10 in the antigen processing can be accounted.     

Identification of sequences in the human peptide transporter subunit TAP1 required for transporter associated with antigen processing (TAP) function

The heterodimeric peptide transporter associated with antigen processing (TAP) consisting of the subunits TAP1 and TAP2 mediates the transport of cytosolic peptides into the lumen of the endoplasmic reticulum (ER). In order to accurately define domains required for peptide transporter function, a molecular approach based on the construction of a panel of human TAP1 mutants and their expression in TAP1(-/-) cells was employed. The characteristics and biological activity of the various TAP1 mutants were determined, and compared to that of wild-type TAP1 and TAP1(-/-) control cells. All mutant TAP1 proteins were localized in the ER and were capable of forming complexes with the TAP2 subunit. However, the TAP1 mutants analyzed transported peptides with different efficiencies and displayed a heterogeneous MHC class I surface expression pattern which was directly associated with their susceptibility to cytotoxic T lymphocyte-mediated lysis. Based on this study, the TAP1 mutants can be divided into three categories: those expressing a similar phenotype compared to TAP1(-/-) or wild-type TAP1 cells respectively, and those representing an intermediate phenotype in terms of peptide transport rate, MHC class I surface expression and immune recognition. Thus, the results provide evidence that specific regions in the TAP1 subunit are crucial for the proper processing and presentation of cytosolic antigens to MHC class I-restricted T cells, whereas others may play a minor role in this process.     

Transporter (TAP)-independent processing of a multiple membrane-spanning protein,the Epstein-Barr virus latent membrane protein 2

Antigen presentation to CD8⁺ cytotoxic T lymphocytes (CTL) usually involves proteolytic cleavage of antigen in the cytosol and the delivery of epitope peptides onto major histocompatibility complex class I molecules in the endoplasmic reticulum (ER) via the heterodimeric peptide transporter TAP1/TAP2. In the few exceptional cases where TAP-independent presentation of an endogenously expressed protein has been observed, the epitope-containing domain of the protein either has naturally accessed or has been directed into the ER lumen where it is thought to become susceptible to ER proteases. Here, we describe a novel example of TAP-independent processing involving the Epstein-Barr virus (EBV) latent membrane protein LMP2, a multiple membrane-spanning protein with minimal projection into the ER. Expression of LMP2 in the TAP⁻ T2 cell line, whether from the resident EBV genome or from a recombinant vaccinia virus vector vacc-LMP2, rendered the cells sensitive to recognition by CTL clones specific for two HLA-A2.1-restricted peptide epitopes, LMP2 329–337 or 426–434. Vacc-LMP2-mediated sensitization to lysis required expression of the antigen de novo in T2 cells and was blocked by brefeldin A. In the same experiments, two other EBV-specific CTL epitopes, one derived from LMP2 but restricted through a different HLA allele (A11), the other restricted through A2.1 but derived from a different viral protein (BMLF1), did not display TAP-independent processing. The results are discussed in relation to the unusual topology of LMP2 in the membrane and the position of the epitope peptides within that structure.     

Interactions formed by individually expressed TAP1 and TAP2 polypeptide subunits

The transporter associated with antigen processing (TAP) supplies peptides into the lumen of the endoplasmic reticulum (ER) for binding by major histocompatibility complex (MHC) class I molecules. TAP comprises two polypeptides, TAP1 and TAP2, each a 'half-transporter' encoding a transmembrane domain and a nucleotide-binding domain. Immunoprecipitation of rat TAP1 and TAP2 expressed individually in the human TAP-deficient cell line, T2, revealed that both bound the endogenously expressed HLA-A2 and -B51 class I molecules. Using HLA-encoding recombinant vaccinia viruses HLA-A*2501, -B*2704, -B*3501 and -B*4402, alleles also associated with both TAP1 and TAP2. Thus, TAP1 and TAP2 do not appear to differ in their ability to interact with MHC class I alleles. Single TAP polypeptide subunits also formed MHC class I peptide-loading complexes, and their nucleotide-binding domains retained the ability to interact with ATP, and may permit the release of peptide-loaded MHC class I molecules in the absence of a peptide transport cycle. It is also demonstrated by chemical cross-linking that TAP2, but not TAP1, has the ability to form a homodimer complex both in whole cells and in detergent lysates. Together these data indicate that single TAP polypeptide subunits possess many of the features of the TAP heterodimer, demonstrating them to be useful models in the study of ATP-binding cassette (ABC) transporters.     

Structural and functional analysis of the TAP-inhibiting UL49.5 proteins of varicelloviruses

Viral infections are counteracted by virus-specific cytotoxic T cells that recognize the infected cell via MHC class I (MHC I) molecules presenting virus-derived peptides. The loading of the peptides onto MHC I molecules occurs in the endoplasmic reticulum (ER) and is facilitated by the peptide loading complex. A key player in this complex is the transporter associated with antigen processing (TAP), which translocates the viral peptides from the cytosol into the ER. Herpesviruses have developed many strategies to evade cytotoxic T cells. Several members of the genus Varicellovirus encode a UL49.5 protein that prevents peptide transport through TAP. These include bovine herpesvirus (BoHV) 1, BoHV-5, bubaline herpesvirus 1, cervid herpesvirus 1, pseudorabies virus, felid herpesvirus 1, and equine herpesvirus 1 and 4. BoHV-1 UL49.5 inhibits TAP by preventing conformational changes essential for peptide transport and by inducing degradation of the TAP complex. UL49.5 consists of an ER luminal N-terminal domain, a transmembrane domain and a cytosolic C-terminal tail domain.In this study, the following features of UL49.5 were deciphered: (1) chimeric constructs of BoHV-1 and VZV UL49.5 attribute the lack of TAP inhibition by VZV UL49.5 to its ER-luminal domain, (2) the ER-luminal and TM domains of UL49.5 are required for efficient interaction with and inhibition of TAP, (3) the C-terminal RXRX sequence is essential for TAP degradation by BoHV-1 UL49.5, and (4) in addition to the RXRX sequence, the cytoplasmic tail of BoHV-1 UL49.5 carries a motif that is required for efficient TAP inhibition by the protein. A model is presented depicting how the different domains of UL49.5 may block the translocation of peptides by TAP and target TAP for proteasomal degradation.     

Association of TAP 1 and 2 gene polymorphisms with human immunodeficiency virus-tuberculosis co-infection

Major histocompatibility complex (MHC) class I binding peptides are carried from cytosol to the lumen of the endoplasmic reticulum (ER) by transporter associated with antigen processing (TAP), an integral ER membrane protein composed of two subunits, TAP1 and TAP2. Polymorphism in TAP genes may influence these proteins further affecting the antigen peptide presentation, indirectly resulting in the viral escape mechanism from cell-mediated immunity in human immunodeficiency virus (HIV). Our aim was to study the influence of these polymorphism in study groups with HIV-tuberculosis (TB) (n = 110), TB (n = 105), and HIV (n = 130) compared with healthy controls (n = 183), using the tetraprimer amplification refractory mutation system (ARMS)-polymerase chain reaction method. Our results demonstrated that the GG genotype at TAP1 position 333 and GA genotype at TAP1 position 637 were positively associated with HIV-TB co-infection and these genotypes may act as a risk factor for developing TB co-infection in HIV-positive individuals.     

TAP-translocated peptides specifically bind proteins in the endoplasmic reticulum,including gp96, protein disulfide isomerase and calreticulin

The endoplasmic reticulum (ER) membrane-embedded transporter associated with antigen processing (TAP) associates with peptides in the cytosol and translocates these into the ER lumen. Here, MHC class I molecules bind a subset of these peptides and the remainder is either removed or degraded, or may be retained in the ER in association with other proteins. We have visualized peptide-binding proteins in the ER using radioactive peptides with a photoreactive group. Besides TAP, two proteins were identified as gp96 and protein disulfide isomerase (PDI). Calreticulin, previously found in complex with TAP, only binds glycosylated peptides. In addition, two as yet unidentified, ER luminal glycoproteins (gp120 and gp170) were visualized. The effects of peptide size and sequence on binding to the ER-resident proteins were studied by using partially degenerated peptides with photoreactive side chains. All identified proteins were able to bind peptides within the size range of peptides translocated by TAP, from 8 to more than 20 amino acids. Whereas PDI associated with all peptides tested, gp96 and gp120 showed a clear sequence preference for non-charged amino acids at positions 2 and 9 in 9mer peptides. Thus various ER proteins, other than the MHC class I heterodimer and TAP, are able to interact with peptides albeit with a different substrate selectivity.     

The ABC-transporter signature motif is required for peptide translocation but not peptide binding by TAP

The transporter associated with antigen processing (TAP) translocates peptides from their site of generation in the cytosol to the lumen of the endoplasmic reticulum for binding to MHC class I molecules. TAP is a member of the ATP-binding cassette (ABC) transporter family whose members utilize energy from ATP hydrolysis to translocate substrates across membranes. The highly conserved nucleotide-binding domains of ABC transporters couple ATP hydrolysis to substrate translocation by the membrane domains. The conserved 'signature motif' can be identified in the nucleotide-binding domains of all ABC transporters, and may play a role in ATP hydrolysis. Here we show that introduction of mutations into the signature motifs of either TAP1 or TAP2 inhibits the translocation of peptide without affecting binding of either peptide or ATP by TAP. We therefore conclude that the signature motifs in both TAP1 and TAP2 are required after peptide binding to facilitate peptide translocation by TAP.     

TAP polymorphism does not influence transport of peptide variants in mice and humans

The major histocompatibility complex (MHC)-encoded transporter associated with antigen processing (TAP) delivers cytosolic peptides to the lumen of the endoplasmic reticulum (ER) for presentation by MHC class I molecules. For the rat, it has been demonstrated that TAP polymorphism results in the selection of different sets of peptides, the nature of the C terminus being of particular importance. Here, we investigated whether TAP polymorphism in mice and humans has functional consequences for transport of peptide sets variable at the C-terminal residues. Using cell lines of H-2^d, H-2^k, and H-2^dxk haplotype and a panel of human lymphoblastoid cell lines expressing eight different TAP alleles, we detected species-specific transport patterns, but no significant influence of TAP polymorphism on peptide selection. In addition, peptides with different core sequences were translocated to the same extent by different TAP. These results suggest that a major contribution of human TAP polymorphism to disease progression and autoimmunity is not very likely.