1
|
Huang Z. Evidence that Alzheimer's Disease Is a Disease of Competitive Synaptic Plasticity Gone Awry. J Alzheimers Dis 2024; 99:447-470. [PMID: 38669548 PMCID: PMC11119021 DOI: 10.3233/jad-240042] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/28/2024]
Abstract
Mounting evidence indicates that a physiological function of amyloid-β (Aβ) is to mediate neural activity-dependent homeostatic and competitive synaptic plasticity in the brain. I have previously summarized the lines of evidence supporting this hypothesis and highlighted the similarities between Aβ and anti-microbial peptides in mediating cell/synapse competition. In cell competition, anti-microbial peptides deploy a multitude of mechanisms to ensure both self-protection and competitor elimination. Here I review recent studies showing that similar mechanisms are at play in Aβ-mediated synapse competition and perturbations in these mechanisms underpin Alzheimer's disease (AD). Specifically, I discuss evidence that Aβ and ApoE, two crucial players in AD, co-operate in the regulation of synapse competition. Glial ApoE promotes self-protection by increasing the production of trophic monomeric Aβ and inhibiting its assembly into toxic oligomers. Conversely, Aβ oligomers, once assembled, promote the elimination of competitor synapses via direct toxic activity and amplification of "eat-me" signals promoting the elimination of weak synapses. I further summarize evidence that neuronal ApoE may be part of a gene regulatory network that normally promotes competitive plasticity, explaining the selective vulnerability of ApoE expressing neurons in AD brains. Lastly, I discuss evidence that sleep may be key to Aβ-orchestrated plasticity, in which sleep is not only induced by Aβ but is also required for Aβ-mediated plasticity, underlining the link between sleep and AD. Together, these results strongly argue that AD is a disease of competitive synaptic plasticity gone awry, a novel perspective that may promote AD research.
Collapse
Affiliation(s)
- Zhen Huang
- Departments of Neuroscience and Neurology, University of Wisconsin-Madison, Madison, WI, USA
| |
Collapse
|
2
|
Zhang S, Kim KB, Huang Y, Kim DW, Kim B, Ko KP, Zou G, Zhang J, Jun S, Kirk NA, Hwang YE, Ban YH, Chan JM, Rudin CM, Park KS, Park JI. CRACD loss promotes small cell lung cancer tumorigenesis via EZH2-mediated immune evasion. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.02.15.528365. [PMID: 36824957 PMCID: PMC9949038 DOI: 10.1101/2023.02.15.528365] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/18/2023]
Abstract
The mechanisms underlying immune evasion and immunotherapy resistance in small cell lung cancer (SCLC) remain unclear. Herein, we investigate the role of CRACD tumor suppressor in SCLC. We found that CRACD is frequently inactivated in SCLC, and Cracd knockout (KO) significantly accelerates SCLC development driven by loss of Rb1, Trp53, and Rbl2. Notably, the Cracd-deficient SCLC tumors display CD8+ T cell depletion and suppression of antigen presentation pathway. Mechanistically, CRACD loss silences the MHC-I pathway through EZH2. EZH2 blockade is sufficient to restore the MHC-I pathway and inhibit CRACD loss-associated SCLC tumorigenesis. Unsupervised single-cell transcriptomic analysis identifies SCLC patient tumors with concomitant inactivation of CRACD, impairment of tumor antigen presentation, and downregulation of EZH2 target genes. Our findings define CRACD loss as a new molecular signature associated with immune evasion of SCLC cells and proposed EZH2 blockade as a viable option for CRACD-negative SCLC treatment.
Collapse
Affiliation(s)
- Shengzhe Zhang
- Department of Experimental Radiation Oncology, Division of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | - Kee-Beom Kim
- Department of Microbiology, Immunology, and Cancer Biology, University of Virginia School of Medicine, Charlottesville, VA 22908, USA
- BK21 FOUR KNU Creative BioResearch Group, School of Life Sciences, Kyungpook National University, Daegu, 41566, Republic of Korea
| | - Yuanjian Huang
- Department of Experimental Radiation Oncology, Division of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | - Dong-Wook Kim
- Department of Microbiology, Immunology, and Cancer Biology, University of Virginia School of Medicine, Charlottesville, VA 22908, USA
| | - Bongjun Kim
- Department of Experimental Radiation Oncology, Division of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | - Kyung-Pil Ko
- Department of Experimental Radiation Oncology, Division of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | - Gengyi Zou
- Department of Experimental Radiation Oncology, Division of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | - Jie Zhang
- Department of Experimental Radiation Oncology, Division of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | - Sohee Jun
- Department of Experimental Radiation Oncology, Division of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | - Nicole A. Kirk
- Department of Microbiology, Immunology, and Cancer Biology, University of Virginia School of Medicine, Charlottesville, VA 22908, USA
| | - Ye Eun Hwang
- Department of Microbiology, Immunology, and Cancer Biology, University of Virginia School of Medicine, Charlottesville, VA 22908, USA
| | - Young Ho Ban
- Hamatovascular Biology Center, Robert M. Berne Cardiovascular Research Center, University of Virginia School of Medicine, Charlottesville, VA 22908, USA
| | - Joseph M. Chan
- Department of Medicine, Thoracic Oncology Service, Memorial Sloan Kettering Cancer Center, New York, NY 10065, USA
| | - Charles M. Rudin
- Department of Medicine, Thoracic Oncology Service, Memorial Sloan Kettering Cancer Center, New York, NY 10065, USA
| | - Kwon-Sik Park
- Department of Microbiology, Immunology, and Cancer Biology, University of Virginia School of Medicine, Charlottesville, VA 22908, USA
| | - Jae-Il Park
- Department of Experimental Radiation Oncology, Division of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
- Graduate School of Biomedical Sciences, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
- Program in Genetics and Epigenetics, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| |
Collapse
|
3
|
Pharmacological disruption of the MTDH-SND1 complex enhances tumor antigen presentation and synergizes with anti-PD-1 therapy in metastatic breast cancer. NATURE CANCER 2022; 3:60-74. [PMID: 35121988 PMCID: PMC8818088 DOI: 10.1038/s43018-021-00280-y] [Citation(s) in RCA: 26] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/20/2020] [Accepted: 09/23/2021] [Indexed: 01/08/2023]
Abstract
Despite increased overall survival rates, curative options for metastatic breast cancer remain limited. We have previously shown that metadherin (MTDH) is frequently overexpressed in poor prognosis breast cancer, where it promotes metastasis and therapy resistance through its interaction with staphylococcal nuclease domain-containing 1 (SND1). Through genetic and pharmacological targeting of the MTDH-SND1 interaction, we reveal a key role for this complex in suppressing antitumor T cell responses in breast cancer. The MTDH-SND1 complex reduces tumor antigen presentation and inhibits T cell infiltration and activation by binding to and destabilizing Tap1/2 messenger RNAs, which encode key components of the antigen-presentation machinery. Following small-molecule compound C26-A6 treatment to disrupt the MTDH-SND1 complex, we showed enhanced immune surveillance and sensitivity to anti-programmed cell death protein 1 therapy in preclinical models of metastatic breast cancer, in support of this combination therapy as a viable approach to increase immune-checkpoint blockade therapy responses in metastatic breast cancer.
Collapse
|
4
|
Wang C, Cao C, Wang N, Wang X, Wang X, Zhang XC. Cryo-electron microscopy structure of human ABCB6 transporter. Protein Sci 2020; 29:2363-2374. [PMID: 33007128 DOI: 10.1002/pro.3960] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2020] [Revised: 09/24/2020] [Accepted: 09/25/2020] [Indexed: 01/12/2023]
Abstract
Human ATP-binding cassette transporter 6 of subfamily B (ABCB6) is an ABC transporter involved in the translocation toxic metals and anti-cancer drugs. Using cryo-electron microscopy, we determined the molecular structure of full-length ABCB6 in an apo state. The structure of ABCB6 unravels the architecture of a full-length ABCB transporter that harbors two N-terminal transmembrane domains which is indispensable for its ATPase activity in our in vitro assay. A slit-like substrate binding pocket of ABCB6 may accommodate the planar shape of porphyrins, and the existence of a secondary cavity near the mitochondrial intermembrane space side would further facilitate substrate release. Furthermore, the ATPase activity of ABCB6 stimulated with a variety of porphyrin substrates showed different profiles in the presence of glutathione (GSH), suggesting the action of a distinct substrate translocation mechanism depending on the use of GSH as a cofactor.
Collapse
Affiliation(s)
- Chunyu Wang
- National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China.,College of Life Sciences, University of Chinese Academy of Sciences, Beijing, China
| | - Can Cao
- National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China.,College of Life Sciences, University of Chinese Academy of Sciences, Beijing, China
| | - Nan Wang
- National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China.,College of Life Sciences, University of Chinese Academy of Sciences, Beijing, China
| | - Xiangxi Wang
- National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China.,College of Life Sciences, University of Chinese Academy of Sciences, Beijing, China
| | - Xianping Wang
- National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China.,College of Life Sciences, University of Chinese Academy of Sciences, Beijing, China
| | - Xuejun C Zhang
- National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China.,College of Life Sciences, University of Chinese Academy of Sciences, Beijing, China
| |
Collapse
|
5
|
Graham M, Tzika AC, Mitchell SM, Liu X, Leonhardt RM. Repeat domain-associated O-glycans govern PMEL fibrillar sheet architecture. Sci Rep 2019; 9:6101. [PMID: 30988362 PMCID: PMC6465243 DOI: 10.1038/s41598-019-42571-6] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2018] [Accepted: 02/06/2019] [Indexed: 12/20/2022] Open
Abstract
PMEL is a pigment cell-specific protein that forms a functional amyloid matrix in melanosomes. The matrix consists of well-separated fibrillar sheets on which the pigment melanin is deposited. Using electron tomography, we demonstrate that this sheet architecture is governed by the PMEL repeat (RPT) domain, which associates with the amyloid as an accessory proteolytic fragment. Thus, the RPT domain is dispensable for amyloid formation as such but shapes the morphology of the matrix, probably in order to maximize the surface area available for pigment adsorption. Although the primary amino acid sequence of the RPT domain differs vastly among various vertebrates, we show that it is a functionally conserved, interchangeable module. RPT domains of all species are predicted to be very highly O-glycosylated, which is likely the common defining feature of this domain. O-glycosylation is indeed essential for RPT domain function and the establishment of the PMEL sheet architecture. Thus, O-glycosylation, not amino acid sequence, appears to be the major factor governing the characteristic PMEL amyloid morphology.
Collapse
Affiliation(s)
- Morven Graham
- Department of Cell Biology, Yale University School of Medicine, 333 Cedar Street, New Haven, CT, 06519, USA
| | - Athanasia C Tzika
- Department of Genetics & Evolution, Laboratory of Artificial & Natural Evolution (LANE), Sciences III Building, 1211, Geneva, 4, Switzerland
| | - Susan M Mitchell
- Department of Immunobiology, Yale University School of Medicine, 300 Cedar Street, New Haven, CT, 06519, USA
| | - Xinran Liu
- Department of Cell Biology, Yale University School of Medicine, 333 Cedar Street, New Haven, CT, 06519, USA
| | - Ralf M Leonhardt
- Department of Immunobiology, Yale University School of Medicine, 300 Cedar Street, New Haven, CT, 06519, USA.
| |
Collapse
|
6
|
Sever L, Vo NTK, Bols NC, Dixon B. Tapasin's protein interactions in the rainbow trout peptide-loading complex. DEVELOPMENTAL AND COMPARATIVE IMMUNOLOGY 2018; 81:262-270. [PMID: 29253558 DOI: 10.1016/j.dci.2017.12.015] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/30/2017] [Revised: 12/14/2017] [Accepted: 12/14/2017] [Indexed: 06/07/2023]
Abstract
Major histocompatibility complex (MHC) class I receptors play a key role in the immune system by presenting non-self peptides to T cell lymphocytes. In humans, the assembly of the MHC class I with a peptide is mediated by machinery in the endoplasmic reticulum referred as the peptide loading complex (PLC). Although, the identity of the PLC has been widely explored in humans, this complex has not been characterized in fish. Co-immunoprecipitation and mass spectrometry analysis revealed that the protein-protein interactions which exist in the human PLC are conserved in the monocyte/macrophage rainbow trout cell line (RTS11), in particular the interaction of tapasin with the transporter associated with antigen processing (TAP), MHC class I and ERp57. Importantly, a 20 kDa tapasin version that contains an intact C and N terminal domains was found to associate with ERp57 and form a 75 kDa heterodimer. These results suggest a possible novel alternative spliced version of tapasin may regulate the formation of the peptide-loading complex in teleosts.
Collapse
Affiliation(s)
- Lital Sever
- Department of Biology, University of Waterloo, 200 University Ave W. Waterloo, Ontario, N2L 3G1, Canada
| | - Nguyen T K Vo
- Department of Biology, University of Waterloo, 200 University Ave W. Waterloo, Ontario, N2L 3G1, Canada
| | - Niels C Bols
- Department of Biology, University of Waterloo, 200 University Ave W. Waterloo, Ontario, N2L 3G1, Canada
| | - Brian Dixon
- Department of Biology, University of Waterloo, 200 University Ave W. Waterloo, Ontario, N2L 3G1, Canada.
| |
Collapse
|
7
|
A highly conserved sequence of the viral TAP inhibitor ICP47 is required for freezing of the peptide transport cycle. Sci Rep 2017; 7:2933. [PMID: 28592828 PMCID: PMC5462769 DOI: 10.1038/s41598-017-02994-5] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2016] [Accepted: 04/21/2017] [Indexed: 12/21/2022] Open
Abstract
The transporter associated with antigen processing (TAP) translocates antigenic peptides into the endoplasmic reticulum (ER) lumen for loading onto MHC class I molecules. This is a key step in the control of viral infections through CD8+ T-cells. The herpes simplex virus type-1 encodes an 88 amino acid long species-specific TAP inhibitor, ICP47, that functions as a high affinity competitor for the peptide binding site on TAP. It has previously been suggested that the inhibitory function of ICP47 resides within the N-terminal region (residues 1–35). Here we show that mutation of the highly conserved 50PLL52 motif within the central region of ICP47 attenuates its inhibitory capacity. Taking advantage of the human cytomegalovirus-encoded TAP inhibitor US6 as a luminal sensor for conformational changes of TAP, we demonstrated that the 50PLL52 motif is essential for freezing of the TAP conformation. Moreover, hierarchical functional interaction sites on TAP dependent on 50PLL52 could be defined using a comprehensive set of human-rat TAP chimeras. This data broadens our understanding of the molecular mechanism underpinning TAP inhibition by ICP47, to include the 50PLL52 sequence as a stabilizer that tethers the TAP-ICP47 complex in an inward-facing conformation.
Collapse
|
8
|
Lapenna A, Omar I, Berger M. A novel spontaneous mutation in the TAP2 gene unravels its role in macrophage survival. Immunology 2016; 150:432-443. [PMID: 27861817 DOI: 10.1111/imm.12694] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2016] [Revised: 11/10/2016] [Accepted: 11/10/2016] [Indexed: 12/20/2022] Open
Abstract
We report a new mouse strain with a single point mutation in the type 2 transporter associated with antigen processing (TAP2). This strain randomly arose in one of our C57BL/6J mouse colonies and was initially discovered because of the lack of CD8+ T cells in the periphery. Following our observation, we subsequently revealed a lack of cell surface MHC-I expression, derived from TAP2 protein deficiency. Our strain, named eightless, has a C to T substitution in exon 5 resulting in a glutamine to stop codon substitution at position 285 in the TAP2 protein. Interestingly, in addition to the expected lack of CD8+ T cell phenotype, eightless mice have a diminished number of macrophages in their peritoneum. Moreover, following peritoneal inflammation, elicited eightless macrophages showed impaired survival both in vivo and ex vivo. Our study describes the first ever TAP2 complete knockout mouse strain and provides a possible explanation for why patients with TAP2 deficiency syndrome present clinical manifestations that would suggest a phagocyte defect rather than a lack of CD8+ T cells.
Collapse
Affiliation(s)
- Antonio Lapenna
- The Lautenberg Centre for Immunology and Cancer Research, The Biomedical Research Institute Israel-Canada of the Faculty of Medicine, The Hebrew University Hadassah Medical School, Jerusalem, Israel
| | - Ibrahim Omar
- The Lautenberg Centre for Immunology and Cancer Research, The Biomedical Research Institute Israel-Canada of the Faculty of Medicine, The Hebrew University Hadassah Medical School, Jerusalem, Israel
| | - Michael Berger
- The Lautenberg Centre for Immunology and Cancer Research, The Biomedical Research Institute Israel-Canada of the Faculty of Medicine, The Hebrew University Hadassah Medical School, Jerusalem, Israel
| |
Collapse
|
9
|
Oldham ML, Hite RK, Steffen AM, Damko E, Li Z, Walz T, Chen J. A mechanism of viral immune evasion revealed by cryo-EM analysis of the TAP transporter. Nature 2016; 529:537-40. [PMID: 26789246 PMCID: PMC4848044 DOI: 10.1038/nature16506] [Citation(s) in RCA: 94] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2015] [Accepted: 12/01/2015] [Indexed: 02/07/2023]
Abstract
Cellular immunity against viral infection and tumor cells depends on antigen presentation by the major histocompatibility complex class 1 molecules (MHC I). Intracellular antigenic peptides are transported into the endoplasmic reticulum (ER) by the transporter associated with antigen processing (TAP) and then loaded onto the nascent MHC I, which are exported to the cell surface and present peptides to the immune system1. Cytotoxic T lymphocytes recognize non-self peptides and program the infected or malignant cells for apoptosis. Defects in TAP account for immunodeficiency and tumor development. To escape immune surveillance, some viruses have evolved strategies to either down-regulate TAP expression or directly inhibit TAP activity. To date neither the architecture of TAP nor the mechanism of viral inhibition has been elucidated at the structural level. In this study we describe the cryo-electron microscopy (cryo-EM) structure of human TAP in complex with its inhibitor ICP47, a small protein produced by the herpes simplex virus I. We show that the twelve transmembrane helices and two cytosolic nucleotide-binding domains (NBDs) of the transporter adopt an inward-facing conformation with the two NBDs separated. The viral inhibitor ICP47 forms a long helical hairpin, which plugs the translocation pathway of TAP from the cytoplasmic side. Association of ICP47 precludes substrate binding and also prevents NBD closure necessary for ATP hydrolysis. This work illustrates a striking example of immune evasion by persistent viruses. By blocking viral antigens from entering the ER, herpes simplex virus is hidden from cytotoxic T lymphocytes, which may contribute to establishing a lifelong infection in the host.
Collapse
Affiliation(s)
- Michael L Oldham
- The Rockefeller University, 1230 York Avenue, New York, New York 10065, USA.,Howard Hughes Medical Institute, 4000 Jones Bridge Road, Chevy Chase, Maryland 20815, USA
| | - Richard K Hite
- The Rockefeller University, 1230 York Avenue, New York, New York 10065, USA.,Howard Hughes Medical Institute, 4000 Jones Bridge Road, Chevy Chase, Maryland 20815, USA
| | - Alanna M Steffen
- Howard Hughes Medical Institute, 4000 Jones Bridge Road, Chevy Chase, Maryland 20815, USA
| | - Ermelinda Damko
- The Rockefeller University, 1230 York Avenue, New York, New York 10065, USA
| | - Zongli Li
- Howard Hughes Medical Institute, 4000 Jones Bridge Road, Chevy Chase, Maryland 20815, USA.,Department of Cell Biology, Harvard Medical School, 240 Longwood Avenue, Boston, Massachusetts 02115, USA
| | - Thomas Walz
- The Rockefeller University, 1230 York Avenue, New York, New York 10065, USA
| | - Jue Chen
- The Rockefeller University, 1230 York Avenue, New York, New York 10065, USA.,Howard Hughes Medical Institute, 4000 Jones Bridge Road, Chevy Chase, Maryland 20815, USA
| |
Collapse
|
10
|
Ma W, Zhang Y, Vigneron N, Stroobant V, Thielemans K, van der Bruggen P, Van den Eynde BJ. Long-Peptide Cross-Presentation by Human Dendritic Cells Occurs in Vacuoles by Peptide Exchange on Nascent MHC Class I Molecules. THE JOURNAL OF IMMUNOLOGY 2016; 196:1711-20. [PMID: 26792804 DOI: 10.4049/jimmunol.1501574] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/13/2015] [Accepted: 12/14/2015] [Indexed: 12/21/2022]
Abstract
Cross-presentation enables dendritic cells to present on their MHC class I molecules antigenic peptides derived from exogenous material, through a mechanism that remains partly unclear. It is particularly efficient with long peptides, which are used in cancer vaccines. We studied the mechanism of long-peptide cross-presentation using human dendritic cells and specific CTL clones against melanoma Ags gp100 and Melan-A/MART1. We found that cross-presentation of those long peptides does not depend on the proteasome or the transporter associated with Ag processing, and therefore follows a vacuolar pathway. We also observed that it makes use of newly synthesized MHC class I molecules, through peptide exchange in vesicles distinct from the endoplasmic reticulum and classical secretory pathway, in an SEC22b- and CD74-independent manner. Our results indicate a nonclassical secretion pathway followed by nascent HLA-I molecules that are used for cross-presentation of those long melanoma peptides in the vacuolar pathway. Our results may have implications for the development of vaccines based on long peptides.
Collapse
Affiliation(s)
- Wenbin Ma
- Ludwig Institute for Cancer Research, Brussels B-1200, Belgium; Walloon Excellence in Life Sciences and Biotechnology, Brussels B-1200, Belgium; de Duve Institute, Université Catholique de Louvain, Brussels B-1200, Belgium
| | - Yi Zhang
- Ludwig Institute for Cancer Research, Brussels B-1200, Belgium; de Duve Institute, Université Catholique de Louvain, Brussels B-1200, Belgium; The Biotherapy Center, The First Affiliated Hospital of Zhengzhou University, Zhengzhou 450052, Henan, China; Department of Oncology, The First Affiliated Hospital of Zhengzhou University, Zhengzhou 450052, Henan, China; and
| | - Nathalie Vigneron
- Ludwig Institute for Cancer Research, Brussels B-1200, Belgium; Walloon Excellence in Life Sciences and Biotechnology, Brussels B-1200, Belgium; de Duve Institute, Université Catholique de Louvain, Brussels B-1200, Belgium
| | - Vincent Stroobant
- Ludwig Institute for Cancer Research, Brussels B-1200, Belgium; de Duve Institute, Université Catholique de Louvain, Brussels B-1200, Belgium
| | - Kris Thielemans
- Laboratory of Molecular and Cellular Therapy, Department of Physiology and Immunology, Vrije Universiteit Brussel, Brussels B-1090, Belgium
| | - Pierre van der Bruggen
- Ludwig Institute for Cancer Research, Brussels B-1200, Belgium; Walloon Excellence in Life Sciences and Biotechnology, Brussels B-1200, Belgium; de Duve Institute, Université Catholique de Louvain, Brussels B-1200, Belgium
| | - Benoît J Van den Eynde
- Ludwig Institute for Cancer Research, Brussels B-1200, Belgium; Walloon Excellence in Life Sciences and Biotechnology, Brussels B-1200, Belgium; de Duve Institute, Université Catholique de Louvain, Brussels B-1200, Belgium;
| |
Collapse
|
11
|
Role of the N-terminal transmembrane domain in the endo-lysosomal targeting and function of the human ABCB6 protein. Biochem J 2015; 467:127-39. [PMID: 25627919 PMCID: PMC4410673 DOI: 10.1042/bj20141085] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
ATP-binding cassette, subfamily B (ABCB) 6 is a homodimeric ATP-binding cassette (ABC) transporter present in the plasma membrane and in the intracellular organelles. The intracellular localization of ABCB6 has been a matter of debate, as it has been suggested to reside in the mitochondria and the endo-lysosomal system. Using a variety of imaging modalities, including confocal microscopy and EM, we confirm the endo-lysosomal localization of ABCB6 and show that the protein is internalized from the plasma membrane through endocytosis, to be distributed to multivesicular bodies and lysosomes. In addition to the canonical nucleotide-binding domain (NBD) and transmembrane domain (TMD), ABCB6 contains a unique N-terminal TMD (TMD0), which does not show sequence homology to known proteins. We investigated the functional role of these domains through the molecular dissection of ABCB6. We find that the folding, dimerization, membrane insertion and ATP binding/hydrolysis of the core–ABCB6 complex devoid of TMD0 are preserved. However, in contrast with the full-length transporter, the core–ABCB6 construct is retained at the plasma membrane and does not appear in Rab5-positive endosomes. TMD0 is directly targeted to the lysosomes, without passage to the plasma membrane. Collectively, our results reveal that TMD0 represents an independently folding unit, which is dispensable for catalysis, but has a crucial role in the lysosomal targeting of ABCB6. The intracellular localization of ATP-binding cassette, sub family B (ABCB) 6 is a matter of debate. We show that ABCB6 is internalized from the plasma membrane to multivesicular bodies and lysosomes. Molecular dissection of the ABCB6 protein reveals a role of its N-terminal domain in targeting.
Collapse
|
12
|
Verweij MC, Horst D, Griffin BD, Luteijn RD, Davison AJ, Ressing ME, Wiertz EJHJ. Viral inhibition of the transporter associated with antigen processing (TAP): a striking example of functional convergent evolution. PLoS Pathog 2015; 11:e1004743. [PMID: 25880312 PMCID: PMC4399834 DOI: 10.1371/journal.ppat.1004743] [Citation(s) in RCA: 68] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Herpesviruses are large DNA viruses that are highly abundant within their host populations. Even in the presence of a healthy immune system, these viruses manage to cause lifelong infections. This persistence is partially mediated by the virus entering latency, a phase of infection characterized by limited viral protein expression. Moreover, herpesviruses have devoted a significant part of their coding capacity to immune evasion strategies. It is believed that the close coexistence of herpesviruses and their hosts has resulted in the evolution of viral proteins that specifically attack multiple arms of the host immune system. Cytotoxic T lymphocytes (CTLs) play an important role in antiviral immunity. CTLs recognize their target through viral peptides presented in the context of MHC molecules at the cell surface. Every herpesvirus studied to date encodes multiple immune evasion molecules that effectively interfere with specific steps of the MHC class I antigen presentation pathway. The transporter associated with antigen processing (TAP) plays a key role in the loading of viral peptides onto MHC class I molecules. This is reflected by the numerous ways herpesviruses have developed to block TAP function. In this review, we describe the characteristics and mechanisms of action of all known virus-encoded TAP inhibitors. Orthologs of these proteins encoded by related viruses are identified, and the conservation of TAP inhibition is discussed. A phylogenetic analysis of members of the family Herpesviridae is included to study the origin of these molecules. In addition, we discuss the characteristics of the first TAP inhibitor identified outside the herpesvirus family, namely, in cowpox virus. The strategies of TAP inhibition employed by viruses are very distinct and are likely to have been acquired independently during evolution. These findings and the recent discovery of a non-herpesvirus TAP inhibitor represent a striking example of functional convergent evolution.
Collapse
Affiliation(s)
- Marieke C. Verweij
- Department of Medical Microbiology, University Medical Center Utrecht, Utrecht, The Netherlands
| | - Daniëlle Horst
- Department of Medical Microbiology, University Medical Center Utrecht, Utrecht, The Netherlands
| | - Bryan D. Griffin
- Department of Medical Microbiology, University Medical Center Utrecht, Utrecht, The Netherlands
| | - Rutger D. Luteijn
- Department of Medical Microbiology, University Medical Center Utrecht, Utrecht, The Netherlands
| | - Andrew J. Davison
- MRC—University of Glasgow Centre for Virus Research, Glasgow, United Kingdom
| | - Maaike E. Ressing
- Department of Medical Microbiology, University Medical Center Utrecht, Utrecht, The Netherlands
| | - Emmanuel J. H. J. Wiertz
- Department of Medical Microbiology, University Medical Center Utrecht, Utrecht, The Netherlands
- * E-mail:
| |
Collapse
|
13
|
Antigen Translocation Machineries in Adaptive Immunity and Viral Immune Evasion. J Mol Biol 2015; 427:1102-18. [DOI: 10.1016/j.jmb.2014.09.006] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2014] [Revised: 09/04/2014] [Accepted: 09/05/2014] [Indexed: 11/23/2022]
|
14
|
Leonhardt RM, Abrahimi P, Mitchell SM, Cresswell P. Three tapasin docking sites in TAP cooperate to facilitate transporter stabilization and heterodimerization. THE JOURNAL OF IMMUNOLOGY 2014; 192:2480-94. [PMID: 24501197 DOI: 10.4049/jimmunol.1302637] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The TAP translocates peptide Ags into the lumen of the endoplasmic reticulum for loading onto MHC class I molecules. MHC class I acquires its peptide cargo in the peptide loading complex, an oligomeric complex that the chaperone tapasin organizes by bridging TAP to MHC class I and recruiting accessory molecules such as ERp57 and calreticulin. Three tapasin binding sites on TAP have been described, two of which are located in the N-terminal domains of TAP1 and TAP2. The third binding site is present in the core transmembrane (TM) domain of TAP1 and is used only by the unassembled subunits. Tapasin is required to promote TAP stability, but through which binding site(s) it is acting is unknown. In particular, the role of tapasin binding to the core TM domain of TAP1 single chains is mysterious because this interaction is lost upon TAP2 association. In this study, we map the respective binding site in TAP1 to the polar face of the amphipathic TM helix TM9 and identify key residues that are essential to establish the interaction. We find that this interaction is dispensable for the peptide transport function but essential to achieve full stability of human TAP1. The interaction is also required for proper heterodimerization of the transporter. Based on similar results obtained using TAP mutants that lack tapasin binding to either N-terminal domain, we conclude that all three tapasin-binding sites in TAP cooperate to achieve high transporter stability and efficient heterodimerization.
Collapse
|
15
|
Chlamydia trachomatis-infected epithelial cells and fibroblasts retain the ability to express surface-presented major histocompatibility complex class I molecules. Infect Immun 2013; 82:993-1006. [PMID: 24343651 DOI: 10.1128/iai.01473-13] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
The obligate intracellular bacterial pathogen Chlamydia trachomatis is the causative agent of a variety of infectious diseases such as trachoma and sexually transmitted diseases. In infected target cells, C. trachomatis replicates within parasitophorous vacuoles and expresses the protease-like activity factor CPAF. Previous studies have suggested that CPAF degrades the host transcription factors RFX5 and NF-κB p65, which are involved in the regulation of constitutive and inducible expression of major histocompatibility complex class I (MHC I). It was speculated that Chlamydia suppresses the surface presentation of MHC I in order to evade an effective immune response. Nevertheless, a recent study suggested that RFX5 and NF-κB p65 may not serve as target substrates for CPAF-mediated degradation, raising concerns about the proposed MHC I subversion by Chlamydia. Hence, we investigated the direct influence of Chlamydia on MHC I expression and surface presentation in infected host cells. By using nine different human cells and cell lines infected with C. trachomatis (serovar D or LGV2), we demonstrate that chlamydial infection does not interfere with expression, maturation, transport, and surface presentation of MHC I, suggesting functional antigen processing in bacterium-infected cells. Our findings provide novel insights into the interaction of chlamydiae with their host cells and should be taken into consideration for the design of future therapies and vaccines.
Collapse
|
16
|
Bomberger JM, Ely KH, Bangia N, Ye S, Green KA, Green WR, Enelow RI, Stanton BA. Pseudomonas aeruginosa Cif protein enhances the ubiquitination and proteasomal degradation of the transporter associated with antigen processing (TAP) and reduces major histocompatibility complex (MHC) class I antigen presentation. J Biol Chem 2013; 289:152-62. [PMID: 24247241 DOI: 10.1074/jbc.m113.459271] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Cif (PA2934), a bacterial virulence factor secreted in outer membrane vesicles by Pseudomonas aeruginosa, increases the ubiquitination and lysosomal degradation of some, but not all, plasma membrane ATP-binding cassette transporters (ABC), including the cystic fibrosis transmembrane conductance regulator and P-glycoprotein. The goal of this study was to determine whether Cif enhances the ubiquitination and degradation of the transporter associated with antigen processing (TAP1 and TAP2), members of the ABC transporter family that play an essential role in antigen presentation and intracellular pathogen clearance. Cif selectively increased the amount of ubiquitinated TAP1 and increased its degradation in the proteasome of human airway epithelial cells. This effect of Cif was mediated by reducing USP10 deubiquitinating activity, resulting in increased polyubiquitination and proteasomal degradation of TAP1. The reduction in TAP1 abundance decreased peptide antigen translocation into the endoplasmic reticulum, an effect that resulted in reduced antigen available to MHC class I molecules for presentation at the plasma membrane of airway epithelial cells and recognition by CD8(+) T cells. Cif is the first bacterial factor identified that inhibits TAP function and MHC class I antigen presentation.
Collapse
Affiliation(s)
- Jennifer M Bomberger
- From the Department of Microbiology and Molecular Genetics, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15219
| | | | | | | | | | | | | | | |
Collapse
|
17
|
The MHC I loading complex: a multitasking machinery in adaptive immunity. Trends Biochem Sci 2013; 38:412-20. [PMID: 23849087 DOI: 10.1016/j.tibs.2013.06.003] [Citation(s) in RCA: 107] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2013] [Revised: 05/31/2013] [Accepted: 06/03/2013] [Indexed: 11/22/2022]
Abstract
Recognition and elimination of virally or malignantly transformed cells are pivotal tasks of the adaptive immune system. For efficient immune detection, snapshots of the cellular proteome are presented as epitopes on major histocompatibility complex class I (MHC I) molecules for recognition by cytotoxic T cells. Knowledge about the track from the equivocal protein to the presentation of antigenic peptides has greatly expanded, leading to an astonishingly elaborate understanding of the MHC I peptide loading pathway. Here, we summarize the current view on this complex process, which involves ABC transporters, proteases, chaperones, and endoplasmic reticulum (ER) quality control. The contribution of individual proteins and subcomplexes is discussed, with a focus on the architecture and dynamics of the key player in the pathway, the peptide-loading complex (PLC).
Collapse
|
18
|
Beutler N, Hauka S, Niepel A, Kowalewski DJ, Uhlmann J, Ghanem E, Erkelenz S, Wiek C, Hanenberg H, Schaal H, Stevanović S, Springer S, Momburg F, Hengel H, Halenius A. A natural tapasin isoform lacking exon 3 modifies peptide loading complex function. Eur J Immunol 2013; 43:1459-69. [DOI: 10.1002/eji.201242725] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2012] [Revised: 02/01/2013] [Accepted: 03/15/2013] [Indexed: 02/06/2023]
Affiliation(s)
- Nele Beutler
- Institute for Virology; Heinrich-Heine-University Düsseldorf; Düsseldorf; Germany
| | - Sebastian Hauka
- Institute for Virology; Heinrich-Heine-University Düsseldorf; Düsseldorf; Germany
| | - Alexandra Niepel
- Institute for Virology; Heinrich-Heine-University Düsseldorf; Düsseldorf; Germany
| | | | - Julia Uhlmann
- Institute for Virology; Heinrich-Heine-University Düsseldorf; Düsseldorf; Germany
| | - Esther Ghanem
- Department of Biochemistry and Cell Biology; Jacobs University Bremen; Bremen; Germany
| | - Steffen Erkelenz
- Institute for Virology; Heinrich-Heine-University Düsseldorf; Düsseldorf; Germany
| | - Constanze Wiek
- Department of Otorhinolaryngology; Heinrich-Heine-University Düsseldorf; Düsseldorf; Germany
| | | | - Heiner Schaal
- Institute for Virology; Heinrich-Heine-University Düsseldorf; Düsseldorf; Germany
| | - Stefan Stevanović
- Department of Immunology; Institute for Cell Biology; University of Tübingen; Tübingen; Germany
| | - Sebastian Springer
- Department of Biochemistry and Cell Biology; Jacobs University Bremen; Bremen; Germany
| | - Frank Momburg
- Division of Translational Immunology (D015); German Cancer Research Center (DKFZ); Heidelberg; Germany
| | | | | |
Collapse
|
19
|
Leonhardt RM, Vigneron N, Hee JS, Graham M, Cresswell P. Critical residues in the PMEL/Pmel17 N-terminus direct the hierarchical assembly of melanosomal fibrils. Mol Biol Cell 2013; 24:964-81. [PMID: 23389629 PMCID: PMC3608505 DOI: 10.1091/mbc.e12-10-0742] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Asp-73, Pro-75, Trp-153, and Trp-160 are essential residues in the PMEL NTR that are required for functional fibril formation. The NTR is necessary in cis to drive the downstream PKD into an amyloid core matrix, which subsequently incorporates and stabilizes the RPT domain–containing, MαC fibril–associated fragment. PMEL (also called Pmel17 or gp100) is a melanocyte/melanoma-specific glycoprotein that plays a critical role in melanosome development by forming a fibrillar amyloid matrix in the organelle for melanin deposition. Although ultimately not a component of mature fibrils, the PMEL N-terminal region (NTR) is essential for their formation. By mutational analysis we establish a high-resolution map of this domain in which sequence elements and functionally critical residues are assigned. We show that the NTR functions in cis to drive the aggregation of the downstream polycystic kidney disease (PKD) domain into a melanosomal core matrix. This is essential to promote in trans the stabilization and terminal proteolytic maturation of the repeat (RPT) domain–containing MαC units, precursors of the second fibrillogenic fragment. We conclude that during melanosome biogenesis the NTR controls the hierarchical assembly of melanosomal fibrils.
Collapse
Affiliation(s)
- Ralf M Leonhardt
- Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, CT, USA.
| | | | | | | | | |
Collapse
|
20
|
Abstract
T cell recognition of antigen-presenting cells depends on their expression of a spectrum of peptides bound to major histocompatibility complex class I (MHC-I) and class II (MHC-II) molecules. Conversion of antigens from pathogens or transformed cells into MHC-I- and MHC-II-bound peptides is critical for mounting protective T cell responses, and similar processing of self proteins is necessary to establish and maintain tolerance. Cells use a variety of mechanisms to acquire protein antigens, from translation in the cytosol to variations on the theme of endocytosis, and to degrade them once acquired. In this review, we highlight the aspects of MHC-I and MHC-II biosynthesis and assembly that have evolved to intersect these pathways and sample the peptides that are produced.
Collapse
Affiliation(s)
- Janice S Blum
- Department of Microbiology and Immunology, Indiana University School of Medicine, Indianapolis, Indiana 46202, USA.
| | | | | |
Collapse
|
21
|
Abstract
The stability of the MHC (major histocompatibility complex) class I peptide repertoire is optimized during assembly in the endoplasmic reticulum (ER) and depends on the collective function of components of the peptide-loading complex (PLC). The chaperone-like molecule tapasin is the cornerstone of this complex and acts directly on the MHC class I molecule to promote high-affinity peptide loading. Optimal tapasin activity, however, relies on the ability of ERp57 and calreticulin, two proteins involved in general ER glycoprotein folding, to bridge and thereby stabilize its otherwise weak interaction with the MHC class I heavy chain. Here, we describe methods for the recombinant expression of soluble components of the PLC specifically tailored to generate the post-translational modifications required to support subcomplex assembly in vitro. Using recombinant MHC class I molecules bearing monoglucosylated N-linked glycans, calreticulin, and disulfide-linked tapasin/ERp57 heterodimers, this soluble PLC subcomplex can be employed to study the mechanism of peptide loading or the principles governing peptide selection for particular MHC class I alleles.
Collapse
Affiliation(s)
- Pamela A Wearsch
- Department of Pathology, Case Western Reserve University, Cleveland, OH, USA
| | - Peter Cresswell
- Department of Immunobiology and Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, USA.
| |
Collapse
|
22
|
Panter MS, Jain A, Leonhardt RM, Ha T, Cresswell P. Dynamics of major histocompatibility complex class I association with the human peptide-loading complex. J Biol Chem 2012; 287:31172-84. [PMID: 22829594 PMCID: PMC3438949 DOI: 10.1074/jbc.m112.387704] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Although the human peptide-loading complex (PLC) is required for optimal major histocompatibility complex class I (MHC I) antigen presentation, its composition is still incompletely understood. The ratio of the transporter associated with antigen processing (TAP) and MHC I to tapasin, which is responsible for MHC I recruitment and peptide binding optimization, is particularly critical for modeling of the PLC. Here, we characterized the stoichiometry of the human PLC using both biophysical and biochemical approaches. By means of single-molecule pulldown (SiMPull), we determined a TAP/tapasin ratio of 1:2, consistent with previous studies of insect-cell microsomes, rat-human chimeric cells, and HeLa cells expressing truncated TAP subunits. We also report that the tapasin/MHC I ratio varies, with the PLC population comprising both 2:1 and 2:2 complexes, based on mutational and co-precipitation studies. The MHC I-saturated PLC may be particularly prevalent among peptide-selective alleles, such as HLA-C4. Additionally, MHC I association with the PLC increases when its peptide supply is reduced by inhibiting the proteasome or by blocking TAP-mediated peptide transport using viral inhibitors. Taken together, our results indicate that the composition of the human PLC varies under normal conditions and dynamically adapts to alterations in peptide supply that may arise during viral infection. These findings improve our understanding of the quality control of MHC I peptide loading and may aid the structural and functional modeling of the human PLC.
Collapse
Affiliation(s)
- Michaela S Panter
- Department of Immunobiology, Yale University School of Medicine, New Haven, Connecticut 06520-8011, USA
| | | | | | | | | |
Collapse
|
23
|
Corradi V, Singh G, Tieleman DP. The human transporter associated with antigen processing: molecular models to describe peptide binding competent states. J Biol Chem 2012; 287:28099-111. [PMID: 22700967 PMCID: PMC3431710 DOI: 10.1074/jbc.m112.381251] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The human transporter associated with antigen processing (TAP) is a member of the ATP binding cassette (ABC) transporter superfamily. TAP plays an essential role in the antigen presentation pathway by translocating cytosolic peptides derived from proteasomal degradation into the endoplasmic reticulum lumen. Here, the peptides are loaded into major histocompatibility class I molecules to be in turn exposed at the cell surface for recognition by T-cells. TAP is a heterodimer formed by the association of two half-transporters, TAP1 and TAP2, with a typical ABC transporter core that consists of two nucleotide binding domains and two transmembrane domains. Despite the availability of biological data, a full understanding of the mechanism of action of TAP is limited by the absence of experimental structures of the full-length transporter. Here, we present homology models of TAP built on the crystal structures of P-glycoprotein, ABCB10, and Sav1866. The models represent the transporter in inward- and outward-facing conformations that could represent initial and final states of the transport cycle, respectively. We described conserved regions in the endoplasmic reticulum-facing loops with a role in the opening and closing of the cavity. We also identified conserved π-stacking interactions in the cytosolic part of the transmembrane domains that could explain the experimental data available for TAP1-Phe-265. Electrostatic potential calculations gave structural insights into the role of residues involved in peptide binding, such as TAP1-Val-288, TAP2-Cys-213, TAP2-Met-218. Moreover, these calculations identified additional residues potentially involved in peptide binding, in turn verified with replica exchange simulations performed on a peptide bound to the inward-facing models.
Collapse
Affiliation(s)
- Valentina Corradi
- Department of Biological Sciences and Institute for Biocomplexity and Informatics, University of Calgary, Calgary, Alberta T2N 1N4, Canada
| | | | | |
Collapse
|
24
|
Stroobant V, Demotte N, Luiten RM, Leonhardt RM, Cresswell P, Bonehill A, Michaux A, Ma W, Mulder A, Van den Eynde BJ, van der Bruggen P, Vigneron N. Inefficient exogenous loading of a tapasin-dependent peptide onto HLA-B*44:02 can be improved by acid treatment or fixation of target cells. Eur J Immunol 2012; 42:1417-28. [PMID: 22678898 PMCID: PMC3766947 DOI: 10.1002/eji.201141954] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Antitumor cytolytic T lymphocytes (CTLs) recognize peptides derived from cellular proteins and presented on MHC class I. One category of peptides recognized by these CTLs is derived from proteins encoded by "cancer-germline" genes, which are specifically expressed in tumors, and therefore represent optimal targets for cancer immunotherapy. Here, we identify an antigenic peptide, which is derived from the MAGE-A1-encoded protein (160-169) and presented to CTLs by HLA-B*44:02. Although this peptide is encoded by MAGE-A1, processed endogenously and presented by tumor cells, the corresponding synthetic peptide is hardly able to sensitize target cells to CTL recognition when pulsed exogenously. Endogenous processing and presentation of this peptide is strictly dependent on the presence of tapasin, which is believed to help peptide loading by stabilizing a peptide-receptive form of HLA-B*44:02. Exogenous loading of the peptide can be dramatically improved by paraformaldehyde fixation of surface molecules or by peptide loading at acidic pH. Either strategy allows efficient exogenous loading of the peptide, presumably by generating or stabilizing a peptide-receptive, empty conformation of the HLA. Altogether, our results indicate a potential drawback of short peptide-based vaccination strategies and offer possible solutions regarding the use of problematic epitopes such as the one described here.
Collapse
Affiliation(s)
- Vincent Stroobant
- Ludwig Institute for Cancer Research, Brussels Branch, Brussels, Belgium
- Welbio and de Duve Institute, Université catholique de Louvain, Brussels, Belgium
| | - Nathalie Demotte
- Ludwig Institute for Cancer Research, Brussels Branch, Brussels, Belgium
- Welbio and de Duve Institute, Université catholique de Louvain, Brussels, Belgium
| | | | - Ralf M. Leonhardt
- Yale University School of Medicine, Department of Immunobiology, 300 Cedar Street, P.O. Box 208011, New Haven CT 06520-8011, USA
| | - Peter Cresswell
- Yale University School of Medicine, Department of Immunobiology, 300 Cedar Street, P.O. Box 208011, New Haven CT 06520-8011, USA
- Howard Hughes Medical Institute
| | - Aude Bonehill
- Laboratory of Molecular and Cellular Therapy, Department of Physiology and Immunology, Medical School of Vrije Universiteit Brussel (VUB), Brussels, Belgium
| | - Alexandre Michaux
- Ludwig Institute for Cancer Research, Brussels Branch, Brussels, Belgium
- Welbio and de Duve Institute, Université catholique de Louvain, Brussels, Belgium
| | - Wenbin Ma
- Ludwig Institute for Cancer Research, Brussels Branch, Brussels, Belgium
- Welbio and de Duve Institute, Université catholique de Louvain, Brussels, Belgium
| | - Arend Mulder
- Department of immunohematology, Leiden University Medical Center, 2333 ZA Leiden, The Netherlands
| | - Benoît J. Van den Eynde
- Ludwig Institute for Cancer Research, Brussels Branch, Brussels, Belgium
- Welbio and de Duve Institute, Université catholique de Louvain, Brussels, Belgium
| | - Pierre van der Bruggen
- Ludwig Institute for Cancer Research, Brussels Branch, Brussels, Belgium
- Welbio and de Duve Institute, Université catholique de Louvain, Brussels, Belgium
| | - Nathalie Vigneron
- Ludwig Institute for Cancer Research, Brussels Branch, Brussels, Belgium
- Welbio and de Duve Institute, Université catholique de Louvain, Brussels, Belgium
| |
Collapse
|
25
|
Direct evidence that the N-terminal extensions of the TAP complex act as autonomous interaction scaffolds for the assembly of the MHC I peptide-loading complex. Cell Mol Life Sci 2012; 69:3317-27. [PMID: 22638925 PMCID: PMC3437018 DOI: 10.1007/s00018-012-1005-6] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2012] [Revised: 04/18/2012] [Accepted: 04/20/2012] [Indexed: 01/01/2023]
Abstract
The loading of antigenic peptides onto major histocompatibility complex class I (MHC I) molecules is an essential step in the adaptive immune response against virally or malignantly transformed cells. The ER-resident peptide-loading complex (PLC) consists of the transporter associated with antigen processing (TAP1 and TAP2), assembled with the auxiliary factors tapasin and MHC I. Here, we demonstrated that the N-terminal extension of each TAP subunit represents an autonomous domain, named TMD0, which is correctly targeted to and inserted into the ER membrane. In the absence of coreTAP, each TMD0 recruits tapasin in a 1:1 stoichiometry. Although the TMD0s lack known ER retention/retrieval signals, they are localized to the ER membrane even in tapasin-deficient cells. We conclude that the TMD0s of TAP form autonomous interaction hubs linking antigen translocation into the ER with peptide loading onto MHC I, hence ensuring a major function in the integrity of the antigen-processing machinery.
Collapse
|
26
|
García-Medel N, Sanz-Bravo A, Barnea E, Admon A, López de Castro JA. The origin of proteasome-inhibitor resistant HLA class I peptidomes: a study with HLA-A*68:01. Mol Cell Proteomics 2011; 11:M111.011486. [PMID: 21969608 DOI: 10.1074/mcp.m111.011486] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Some HLA class I molecules bind a significant fraction of their constitutive peptidomes in the presence of proteasome inhibitors. In this study, A*68:01-bound peptides, and their parental proteins, were characterized through massive mass spectrometry sequencing to refine its binding motif, including the nearly exclusive preference for C-terminal basic residues. Stable isotope tagging was used to distinguish proteasome-inhibitor sensitive and resistant ligands. The latter accounted for less than 20% of the peptidome and, like in HLA-B27, arose predominantly from small and basic proteins. Under the conditions used for proteasome inhibition in vivo, epoxomicin and MG-132 incompletely inhibited the hydrolysis of fluorogenic substrates specific for the tryptic or for both the tryptic and chymotryptic subspecificities, respectively. This incomplete inhibition was also reflected in the cleavage of synthetic peptide precursors of A*68:01 ligands. For these substrates, the inhibition of the proteasome resulted in altered cleavage patterns. However these alterations did not upset the balance between cleavage at peptide bonds resulting in epitope destruction and those leading to their generation. The results indicate that inhibitor-resistant HLA class I ligands are not necessarily produced by non-proteasomal pathways. However, their generation is not simply explained by decreased epitope destruction upon incomplete proteasomal inhibition and may require additional proteolytic steps acting on incompletely processed proteasomal products.
Collapse
Affiliation(s)
- Noel García-Medel
- Centro de Biología Molecular Severo Ochoa (Consejo Superior de Investigaciones Científicas and Universidad Autónoma de Madrid), c/ Nicolas Cabrera N.1, Universidad Autónoma, 28049 Madrid, Spain
| | - Alejandro Sanz-Bravo
- Centro de Biología Molecular Severo Ochoa (Consejo Superior de Investigaciones Científicas and Universidad Autónoma de Madrid), c/ Nicolas Cabrera N.1, Universidad Autónoma, 28049 Madrid, Spain
| | - Eilon Barnea
- Faculty of Biology, Technion - Israel Institute of Technology, Haifa 32000, Israel
| | - Arie Admon
- Faculty of Biology, Technion - Israel Institute of Technology, Haifa 32000, Israel
| | - José A López de Castro
- Centro de Biología Molecular Severo Ochoa (Consejo Superior de Investigaciones Científicas and Universidad Autónoma de Madrid), c/ Nicolas Cabrera N.1, Universidad Autónoma, 28049 Madrid, Spain.
| |
Collapse
|
27
|
Van Hateren A, James E, Bailey A, Phillips A, Dalchau N, Elliott T. The cell biology of major histocompatibility complex class I assembly: towards a molecular understanding. ACTA ACUST UNITED AC 2011; 76:259-75. [PMID: 21050182 DOI: 10.1111/j.1399-0039.2010.01550.x] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Major histocompatibility complex class I (MHC I) proteins protect the host from intracellular pathogens and cellular abnormalities through the binding of peptide fragments derived primarily from intracellular proteins. These peptide-MHC complexes are displayed at the cell surface for inspection by cytotoxic T lymphocytes. Here we reveal how MHC I molecules achieve this feat in the face of numerous levels of quality control. Among these is the chaperone tapasin, which governs peptide selection in the endoplasmic reticulum as part of the peptide-loading complex, and we propose key amino acid interactions central to the peptide selection mechanism. We discuss how the aminopeptidase ERAAP fine-tunes the peptide repertoire available to assembling MHC I molecules, before focusing on the journey of MHC I molecules through the secretory pathway, where calreticulin provides additional regulation of MHC I expression. Lastly we discuss how these processes culminate to influence immune responses.
Collapse
Affiliation(s)
- A Van Hateren
- Faculty of Medicine, Southampton General Hospital, University of Southampton, Southampton, UK
| | | | | | | | | | | |
Collapse
|
28
|
Leonhardt RM, Vigneron N, Rahner C, Cresswell P. Proprotein convertases process Pmel17 during secretion. J Biol Chem 2011; 286:9321-37. [PMID: 21247888 PMCID: PMC3059051 DOI: 10.1074/jbc.m110.168088] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Pmel17 is a melanocyte/melanoma-specific protein that traffics to melanosomes where it forms a fibrillar matrix on which melanin gets deposited. Before being cleaved into smaller fibrillogenic fragments the protein undergoes processing by proprotein convertases, a class of serine proteases that typically recognize the canonical motif RX(R/K)R↓. The current model of Pmel17 maturation states that this processing step occurs in melanosomes, but in light of recent reports this issue has become controversial. We therefore addressed this question by thoroughly assessing the processing kinetics of either wild-type Pmel17 or a secreted soluble Pmel17 derivative. Our results demonstrate clearly that processing of Pmel17 occurs during secretion and that it does not require entry of the protein into the endocytic system. Strikingly, processing proceeds even in the presence of the secretion inhibitor monensin, suggesting that Pmel17 is an exceptionally good substrate. In line with this, we find that newly synthesized surface Pmel17 is already quantitatively cleaved. Moreover, we demonstrate that Pmel17 function is independent of the sequence identity of its unconventional proprotein convertase-cleavage motif that lacks arginine in P4 position. The data alter the current view of Pmel17 maturation and suggest that the multistep processing of Pmel17 begins with an early cleavage during secretion that primes the protein for later functional processing.
Collapse
Affiliation(s)
- Ralf M Leonhardt
- Department of Immunobiology, Yale University School of Medicine, New Haven, Connecticut 06519, USA.
| | | | | | | |
Collapse
|
29
|
Ghanem E, Fritzsche S, Al-Balushi M, Hashem J, Ghuneim L, Thomer L, Kalbacher H, van Endert P, Wiertz E, Tampé R, Springer S. The transporter associated with antigen processing (TAP) is active in a post-ER compartment. J Cell Sci 2010; 123:4271-9. [DOI: 10.1242/jcs.060632] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
The translocation of cytosolic peptides into the lumen of the endoplasmic reticulum (ER) is a crucial step in the presentation of intracellular antigen to T cells by major histocompatibility complex (MHC) class I molecules. It is mediated by the transporter associated with antigen processing (TAP) protein, which binds to peptide-receptive MHC class I molecules to form the MHC class I peptide-loading complex (PLC). We investigated whether TAP is present and active in compartments downstream of the ER. By fluorescence microscopy, we found that TAP is localized to the ERGIC (ER-Golgi intermediate compartment) and the Golgi of both fibroblasts and lymphocytes. Using an in vitro vesicle formation assay, we show that COPII vesicles, which carry secretory cargo out of the ER, contain functional TAP that is associated with MHC class I molecules. Together with our previous work on post-ER localization of peptide-receptive class I molecules, our results suggest that loading of peptides onto class I molecules in the context of the peptide-loading complex can occur outside the ER.
Collapse
Affiliation(s)
- Esther Ghanem
- Biochemistry and Cell Biology, Molecular Life Science Center, Jacobs University Bremen, 28759 Bremen, Germany
| | - Susanne Fritzsche
- Biochemistry and Cell Biology, Molecular Life Science Center, Jacobs University Bremen, 28759 Bremen, Germany
| | - Mohammed Al-Balushi
- Biochemistry and Cell Biology, Molecular Life Science Center, Jacobs University Bremen, 28759 Bremen, Germany
- Department of Microbiology and Immunology, Sultan Qaboos University, Muscat 123, Oman
| | - Jood Hashem
- Biochemistry and Cell Biology, Molecular Life Science Center, Jacobs University Bremen, 28759 Bremen, Germany
| | - Lana Ghuneim
- Biochemistry and Cell Biology, Molecular Life Science Center, Jacobs University Bremen, 28759 Bremen, Germany
| | - Lena Thomer
- Biochemistry and Cell Biology, Molecular Life Science Center, Jacobs University Bremen, 28759 Bremen, Germany
| | - Hubert Kalbacher
- Medical and Natural Sciences Research Center, University of Tübingen, 72074 Tübingen, Germany
| | - Peter van Endert
- INSERM, U580, 75015 Paris, France, and Université Paris Descartes, Faculté de Médecine René Descartes, 75015 Paris, France
| | - Emmanuel Wiertz
- Department of Medical Microbiology, University Medical Centre Utrecht, Heidelberglaan 100, 3584 CX Utrecht, and Department of Medical Microbiology, Leiden University Medical Center, PO Box 9600, 2300 RC Leiden, The Netherlands
| | - Robert Tampé
- Cluster of Excellence ‘Macromolecular Complexes’, Institute of Biochemistry, Biocenter, Goethe University Frankfurt, Marie-Curie-Str. 9, 60439 Frankfurt, Germany
| | - Sebastian Springer
- Biochemistry and Cell Biology, Molecular Life Science Center, Jacobs University Bremen, 28759 Bremen, Germany
| |
Collapse
|
30
|
Zhu Y, Zhang W, Veerapen N, Besra G, Cresswell P. Calreticulin controls the rate of assembly of CD1d molecules in the endoplasmic reticulum. J Biol Chem 2010; 285:38283-92. [PMID: 20861015 PMCID: PMC2992262 DOI: 10.1074/jbc.m110.170530] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
CD1d is an MHC class I-like molecule comprised of a transmembrane glycoprotein (heavy chain) associated with β2-microglobulin (β2m) that presents lipid antigens to NKT cells. Initial folding of the heavy chain involves its glycan-dependent association with calreticulin (CRT), calnexin (CNX), and the thiol oxidoreductase ERp57, and is followed by assembly with β2m to form the heterodimer. Here we show that in CRT-deficient cells CD1d heavy chains convert to β2m-associated dimers at an accelerated rate, indicating faster folding of the heavy chain, while the rate of intracellular transport after assembly is unaffected. Unlike the situation with MHC class I molecules, antigen presentation by CD1d is not impaired in the absence of CRT. Instead, there are elevated levels of stable and functional CD1d on the surface of CRT-deficient cells. Association of the heavy chains with the ER chaperones Grp94 and Bip is observed in the absence of CRT, and these may replace CRT in mediating CD1d folding and assembly. ER retention of free CD1d heavy chains is impaired in CRT-deficient cells, allowing their escape and subsequent expression on the plasma membrane. However, these free heavy chains are rapidly internalized and degraded in lysosomes, indicating that β2m association is required for the exceptional resistance of CD1d to lysosomal degradation that is normally observed.
Collapse
Affiliation(s)
- Yajuan Zhu
- Department of Immunobiology, Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, Connecticut 06520-8011, USA
| | | | | | | | | |
Collapse
|
31
|
Demirel O, Bangert I, Tampé R, Abele R. Tuning the cellular trafficking of the lysosomal peptide transporter TAPL by its N-terminal domain. Traffic 2010; 11:383-93. [PMID: 20377823 DOI: 10.1111/j.1600-0854.2009.01021.x] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The homodimeric ATP-binding cassette (ABC) transport complex TAPL (transporter associated with antigen processing-like, ABCB9) translocates a broad spectrum of peptides from the cytosol into the lumen of lysosomes. The presence of an extra N-terminal transmembrane domain (TMD0) lacking any sequence homology to known proteins distinguishes TAPL from most other ABC transporters of its subfamily. By dissecting TAPL, we could assign distinct functions to the core complex and TMD0. The core-TAPL complex, composed of six predicted transmembrane helices and a nucleotide-binding domain, is sufficient for peptide transport, showing that the core transport complex is correctly targeted to and assembled in the membrane. Strikingly, in contrast to the full-length transporter, the core translocation complex is targeted preferentially to the plasma membrane. However, TMD0 alone, comprising a putative four transmembrane helix bundle, traffics to lysosomes. Upon coexpression, TMD0 forms a stable non-covalently linked complex with the core translocation machinery and guides core-TAPL into lysosomal compartments. Therefore, TMD0 represents a unique domain, which folds independently and encodes the information for lysosomal targeting. These outcomes are discussed in respect of trafficking, folding and function of TAPL.
Collapse
Affiliation(s)
- Ozlem Demirel
- Institute of Biochemistry, Biocenter, Goethe-University Frankfurt, Max-von-Laue-Str. 9, D-60438 Frankfurt am Main, Germany
| | | | | | | |
Collapse
|
32
|
Abstract
How ABC transporters work is a key issue because of their important roles in multidrug resistance of pathogenic bacteria, reduced efficacy of antitumor drugs, cholesterol metabolism, cell homeostasis and immune response. In the past few years, significant progress has been made in crystallization and structure determination of (mostly) bacterial ABC transporters, as well as in functional studies on ABC systems involved in human pathology. In this review, we use the transporter associated with antigen processing (TAP) to illustrate what is known regarding the mechanism of substrate transport. We also discuss the chemical basis of substrate recognition by TAP and the allosteric cross-talk between the binding of substrate, the release of chemical energy by ATP hydrolysis and cross-membrane translocation. Finally, we detail the role of TAP in a large macromolecular assembly, which optimally loads MHC class I molecules, and the interference with this machinery by TAP-targeted viral factors. Because of structural and probable mechanistic similarities, the understanding of the detailed structure and mechanism of TAP will be applicable to all ABC systems, including those of medical relevance.
Collapse
|
33
|
Abstract
How ABC transporters work is a key issue because of their important roles in multidrug resistance of pathogenic bacteria, reduced efficacy of antitumor drugs, cholesterol metabolism, cell homeostasis and immune response. In the past few years, significant progress has been made in crystallization and structure determination of (mostly) bacterial ABC transporters, as well as in functional studies on ABC systems involved in human pathology. In this review, we use the transporter associated with antigen processing (TAP) to illustrate what is known regarding the mechanism of substrate transport. We also discuss the chemical basis of substrate recognition by TAP and the allosteric cross-talk between the binding of substrate, the release of chemical energy by ATP hydrolysis and cross-membrane translocation. Finally, we detail the role of TAP in a large macromolecular assembly, which optimally loads MHC class I molecules, and the interference with this machinery by TAP-targeted viral factors. Because of structural and probable mechanistic similarities, the understanding of the detailed structure and mechanism of TAP will be applicable to all ABC systems, including those of medical relevance.
Collapse
Affiliation(s)
- David Parcej
- Institute of Biochemistry, Biocenter, Goethe University Frankfurt, Frankfurt, Germany.
| | | |
Collapse
|
34
|
Lundegaard C, Lund O, Buus S, Nielsen M. Major histocompatibility complex class I binding predictions as a tool in epitope discovery. Immunology 2010; 130:309-18. [PMID: 20518827 DOI: 10.1111/j.1365-2567.2010.03300.x] [Citation(s) in RCA: 92] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
SUMMARY Over the last decade, in silico models of the major histocompatibility complex (MHC) class I pathway have developed significantly. Before, peptide binding could only be reliably modelled for a few major human or mouse histocompatibility molecules; now, high-accuracy predictions are available for any human leucocyte antigen (HLA) -A or -B molecule with known protein sequence. Furthermore, peptide binding to MHC molecules from several non-human primates, mouse strains and other mammals can now be predicted. In this review, a number of different prediction methods are briefly explained, highlighting the most useful and historically important. Selected case stories, where these 'reverse immunology' systems have been used in actual epitope discovery, are briefly reviewed. We conclude that this new generation of epitope discovery systems has become a highly efficient tool for epitope discovery, and recommend that the less accurate prediction systems of the past be abandoned, as these are obsolete.
Collapse
Affiliation(s)
- Claus Lundegaard
- Department of Systems Biology, Centre for Biological Sequence Analysis, Technical University of Denmark, Lyngby, Denmark.
| | | | | | | |
Collapse
|
35
|
Leonhardt RM, Vigneron N, Rahner C, Van den Eynde BJ, Cresswell P. Endoplasmic reticulum export, subcellular distribution, and fibril formation by Pmel17 require an intact N-terminal domain junction. J Biol Chem 2010; 285:16166-83. [PMID: 20231267 PMCID: PMC2871485 DOI: 10.1074/jbc.m109.097725] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Pmel17 is a melanocyte/melanoma-specific protein that subcellularly localizes to melanosomes, where it forms a fibrillar matrix that serves for the sequestration of potentially toxic reaction intermediates of melanin synthesis and deposition of the pigment. As a key factor in melanosomal biogenesis, understanding intracellular trafficking and processing of Pmel17 is of central importance to comprehend how these organelles are formed, how they mature, and how they function in the cell. Using a series of deletion and missense mutants of Pmel17, we are able to show that the integrity of the junction between the N-terminal region and the polycystic kidney disease-like domain is highly crucial for endoplasmic reticulum export, subcellular targeting, and fibril formation by Pmel17 and thus for establishing functional melanosomes.
Collapse
Affiliation(s)
- Ralf M Leonhardt
- Department of Immunobiology, Yale University School of Medicine, New Haven, Connecticut 06519, USA.
| | | | | | | | | |
Collapse
|
36
|
Leonhardt RM, Fiegl D, Rufer E, Karger A, Bettin B, Knittler MR. Post-endoplasmic reticulum rescue of unstable MHC class I requires proprotein convertase PC7. THE JOURNAL OF IMMUNOLOGY 2010; 184:2985-98. [PMID: 20164418 DOI: 10.4049/jimmunol.0900308] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The function of the peptide-loading complex (PLC) is to facilitate loading of MHC class I (MHC I) molecules with antigenic peptides in the endoplasmic reticulum and to drive the selection of these ligands toward a set of high-affinity binders. When the PLC fails to perform properly, as frequently observed in virus-infected or tumor cells, structurally unstable MHC I peptide complexes are generated, which are prone to disintegrate instead of presenting Ags to cytotoxic T cells. In this study we show that a second quality control checkpoint dependent on the serine protease proprotein convertase 7 (PC7) can rescue unstable MHC I, whereas the related convertase furin is completely dispensable. Cells with a malfunctioning PLC and silenced for PC7 have substantially reduced MHC I surface levels caused by high instability and significantly delayed surface accumulation of these molecules. Instead of acquiring stability along the secretory route, MHC I appears to get largely routed to lysosomes for degradation in these cells. Moreover, mass spectrometry analysis provides evidence that lack of PLC quality control and/or loss of PC7 expression alters the MHC I-presented peptide profile. Finally, using exogenously applied peptide precursors, we show that liberation of MHC I epitopes may directly require PC7. We demonstrate for the first time an important function for PC7 in MHC I-mediated Ag presentation.
Collapse
Affiliation(s)
- Ralf M Leonhardt
- Department of Immunobiology, Yale University School of Medicine, New Haven, CT 06519, USA
| | | | | | | | | | | |
Collapse
|
37
|
Vigneron N, Peaper DR, Leonhardt RM, Cresswell P. Functional significance of tapasin membrane association and disulfide linkage to ERp57 in MHC class I presentation. Eur J Immunol 2009; 39:2371-6. [PMID: 19701894 DOI: 10.1002/eji.200939536] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Tapasin is disulfide linked to ERp57 within the peptide loading complex. In cell-free assays, a soluble variant of the tapasin/ERp57 dimer recruits MHC class I molecules and promotes peptide binding to them, whereas soluble tapasin alone does not. Here we show that within cells, tapasin conjugation with ERp57 is as critical as its integration into the membrane for efficient MHC class I assembly, surface expression, and Ag presentation to CD8(+) T cells. Elimination of both of these properties severely compromises tapasin function, in keeping with predictions from in vitro studies.
Collapse
Affiliation(s)
- Nathalie Vigneron
- Department of Immunobiology, Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, CT 06520-8011, USA
| | | | | | | |
Collapse
|
38
|
Simone LC, Wang X, Solheim JC. A transmembrane tail: interaction of tapasin with TAP and the MHC class I molecule. Mol Immunol 2009; 46:2147-50. [PMID: 19361863 DOI: 10.1016/j.molimm.2009.03.006] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2009] [Accepted: 03/09/2009] [Indexed: 11/28/2022]
Abstract
The transmembrane protein tapasin has an essential role in the assembly of stable major histocompatibility (MHC) class I/peptide complexes. Within the endoplasmic reticulum, tapasin associates with both the transporter associated with antigen processing (TAP) and the MHC class I molecule. The tapasin/TAP association has been clearly shown to involve the transmembrane domains (TMDs) of both molecules and to result in the stable expression of TAP. Although the influence of tapasin on MHC class I molecule folding and surface expression has been extensively studied, relatively little is known at the structural level regarding the interaction between tapasin and the MHC class I molecule. Here we summarize our current understanding of functions involving the tapasin TMD and propose that, beyond stabilizing TAP, the tapasin TMD may also interact with the MHC class I heavy chain.
Collapse
Affiliation(s)
- Laura C Simone
- Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, Nebraska Medical Center, Omaha, NE 68198-6805, USA
| | | | | |
Collapse
|
39
|
Structural arrangement of the transmission interface in the antigen ABC transport complex TAP. Proc Natl Acad Sci U S A 2009; 106:5551-6. [PMID: 19297616 DOI: 10.1073/pnas.0811260106] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
The transporter associated with antigen processing (TAP) represents a focal point in the immune recognition of virally or malignantly transformed cells by translocating proteasomal degradation products into the endoplasmic reticulum-lumen for loading of MHC class I molecules. Based on a number of experimental data and the homology to the bacterial ABC exporter Sav1866, we constructed a 3D structural model of the core TAP complex and used it to examine the interface between the transmembrane and nucleotide-binding domains (NBD) by cysteine-scanning and cross-linking approaches. Herein, we demonstrate the functional importance of the newly identified X-loop in the NBD in coupling substrate binding to downstream events in the transport cycle. We further verified domain swapping in a heterodimeric ABC half-transporter complex by cysteine cross-linking. Strikingly, either substrate binding or translocation can be blocked by cross-linking the X-loop to coupling helix 2 or 1, respectively. These results resolve the structural arrangement of the transmission interface and point to different functions of the cytosolic loops and coupling helices in substrate binding, signaling, and transport.
Collapse
|
40
|
Raghavan M, Del Cid N, Rizvi SM, Peters LR. MHC class I assembly: out and about. Trends Immunol 2009; 29:436-43. [PMID: 18675588 DOI: 10.1016/j.it.2008.06.004] [Citation(s) in RCA: 80] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2008] [Revised: 06/23/2008] [Accepted: 06/26/2008] [Indexed: 01/06/2023]
Abstract
The assembly of major histocompatibility complex (MHC) class I molecules with peptides is orchestrated by several assembly factors including the transporter associated with antigen processing (TAP) and tapasin, the endoplasmic reticulum (ER) oxido-reductases ERp57 and protein disulfide isomerase (PDI), the lectin chaperones calnexin and calreticulin, and the ER aminopeptidase (ERAAP). Typically, MHC class I molecules present endogenous antigens to cytotoxic T lymphocytes (CTLs). However, the initiation of CD8(+) T-cell responses against many pathogens and tumors also requires the presentation of exogenous antigens by MHC class I molecules. We discuss recent developments relating to interactions and mechanisms of function of the various assembly factors and pathways by which exogenous antigens access MHC class I molecules.
Collapse
Affiliation(s)
- Malini Raghavan
- Department of Microbiology and Immunology, University of Michigan, Ann Arbor, MI 48109, USA.
| | | | | | | |
Collapse
|
41
|
Verweij MC, Koppers-Lalic D, Loch S, Klauschies F, de la Salle H, Quinten E, Lehner PJ, Mulder A, Knittler MR, Tampé R, Koch J, Ressing ME, Wiertz EJHJ. The varicellovirus UL49.5 protein blocks the transporter associated with antigen processing (TAP) by inhibiting essential conformational transitions in the 6+6 transmembrane TAP core complex. THE JOURNAL OF IMMUNOLOGY 2008; 181:4894-907. [PMID: 18802093 DOI: 10.4049/jimmunol.181.7.4894] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
TAP translocates virus-derived peptides from the cytosol into the endoplasmic reticulum, where the peptides are loaded onto MHC class I molecules. This process is crucial for the detection of virus-infected cells by CTL that recognize the MHC class I-peptide complexes at the cell surface. The varicellovirus bovine herpesvirus 1 encodes a protein, UL49.5, that acts as a potent inhibitor of TAP. UL49.5 acts in two ways, as follows: 1) by blocking conformational changes of TAP required for the translocation of peptides into the endoplasmic reticulum, and 2) by targeting TAP1 and TAP2 for proteasomal degradation. At present, it is unknown whether UL49.5 interacts with TAP1, TAP2, or both. The contribution of other members of the peptide-loading complex has not been established. Using TAP-deficient cells reconstituted with wild-type and recombinant forms of TAP1 and TAP2, TAP was defined as the prime target of UL49.5 within the peptide-loading complex. The presence of TAP1 and TAP2 was required for efficient interaction with UL49.5. Using deletion mutants of TAP1 and TAP2, the 6+6 transmembrane core complex of TAP was shown to be sufficient for UL49.5 to interact with TAP and block its function. However, UL49.5-induced inhibition of peptide transport was most efficient in cells expressing full-length TAP1 and TAP2. Inhibition of TAP by UL49.5 appeared to be independent of the presence of other peptide-loading complex components, including tapasin. These results demonstrate that UL49.5 acts directly on the 6+6 transmembrane TAP core complex of TAP by blocking essential conformational transitions required for peptide transport.
Collapse
Affiliation(s)
- Marieke C Verweij
- Department of Medical Microbiology, Center of Infectious Diseases, Leiden University Medical Center, Leiden, The Netherlands
| | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
42
|
Abstract
Peptide binding to MHC class I molecules is a component of a folding and assembly process that occurs in the endoplasmic reticulum (ER) and uses both cellular chaperones and dedicated factors. The involvement of glycoprotein quality-control chaperones and cellular oxidoreductases in peptide binding has led to models that are gradually being refined. Some aspects of the peptide loading process (e.g., the biosynthesis and degradation of MHC class I complexes) conform to models of glycoprotein quality control, but other aspects (e.g., the formation of a stable disulfide-linked dimer between tapasin and ERp57) deviate from models of chaperone and oxidoreductase function. Here we review what is known about the intersection of glycoprotein folding, oxidative reactions, and MHC class I peptide loading, emphasizing events that occur in the ER and within the MHC class I peptide loading complex.
Collapse
Affiliation(s)
- David R Peaper
- Howard Hughes Medical Institute, Department of Immunobiology, Yale University School of Medicine, New Haven, Connecticut 06520, USA.
| | | |
Collapse
|
43
|
The quality control of MHC class I peptide loading. Curr Opin Cell Biol 2008; 20:624-31. [PMID: 18926908 DOI: 10.1016/j.ceb.2008.09.005] [Citation(s) in RCA: 156] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2008] [Revised: 09/16/2008] [Accepted: 09/17/2008] [Indexed: 11/20/2022]
Abstract
The assembly of major histocompatibility complex (MHC) class I molecules is one of the more widely studied examples of protein folding in the endoplasmic reticulum (ER). It is also one of the most unusual cases of glycoprotein quality control involving the thiol oxidoreductase ERp57 and the lectin-like chaperones calnexin and calreticulin. The multistep assembly of MHC class I heavy chain with beta(2)-microglobulin and peptide is facilitated by these ER-resident proteins and further tailored by the involvement of a peptide transporter, aminopeptidases, and the chaperone-like molecule tapasin. Here we summarize recent progress in understanding the roles of these general and class I-specific ER proteins in facilitating the optimal assembly of MHC class I molecules with high affinity peptides for antigen presentation.
Collapse
|
44
|
Antoniou AN, Powis SJ. Pathogen evasion strategies for the major histocompatibility complex class I assembly pathway. Immunology 2008; 124:1-12. [PMID: 18284468 DOI: 10.1111/j.1365-2567.2008.02804.x] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
Major histocompatibility complex (MHC) class I molecules bind and present short antigenic peptides from endogenously or exogenously derived sources to CD8(+) cytotoxic T lymphocytes (CTL), with recognition of a foreign peptide normally targeting the cell for lysis. It is generally thought that the high level of MHC polymorphism, which is concentrated mostly within the peptide-binding groove, is driven by the 'evolutionary arms race' against pathogens. Many pathogens have developed novel and intriguing mechanisms for evading the continuous sampling of the intracellular and intercellular environments by MHC molecules, none more so than viruses. The characterization of immunoevasion mechanisms has improved our understanding of MHC biology. This review will highlight our current understanding of the MHC class I biosynthetic pathway and how it has been exploited by pathogens, especially viruses, to potentially evade CTL recognition.
Collapse
Affiliation(s)
- Antony N Antoniou
- Department of Immunology & Molecular Pathology, Division of Infection & Immunity, University College London, Windeyer Institute of Medical Science, London, UK.
| | | |
Collapse
|
45
|
Structural and Functional Dissection of the Human Cytomegalovirus Immune Evasion Protein US6. J Virol 2008; 82:3271-82. [PMID: 18199642 DOI: 10.1128/jvi.01705-07] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The human cytomegalovirus (HCMV) protein US6 inhibits the transporter associated with antigen processing (TAP). Since TAP transports antigenic peptides into the endoplasmic reticulum for binding to major histocompatibility class I molecules, inhibition of the transporter by HCMV US6 impairs the presentation of viral antigens to cytotoxic T lymphocytes. HCMV US6 inhibits ATP binding by TAP, hence depriving TAP of the energy source it requires for peptide translocation, yet the molecular basis for the interaction between US6 and TAP is poorly understood. In this study we demonstrate that residues 89 to 108 of the HCMV US6 luminal domain are required for TAP inhibition, whereas sequences that flank this region stabilize the binding of the viral protein to TAP. In parallel, we demonstrate that chimpanzee cytomegalovirus (CCMV) US6 binds, but does not inhibit, human TAP. The sequence of CCMV US6 differs from that of HCMV US6 in the region corresponding to residues 89 to 108 of the HCMV protein. The substitution of this region of CCMV US6 with the corresponding residues from HCMV US6 generates a chimeric protein that inhibits human TAP and provides further evidence for the pivotal role of residues 89 to 108 of HCMV US6 in the inhibition of TAP. On the basis of these observations, we propose that there is a hierarchy of interactions between HCMV US6 and TAP, in which residues 89 to 108 of HCMV US6 interact with and inhibit TAP, whereas other parts of the viral protein also bind to TAP and stabilize this inhibitory interaction.
Collapse
|
46
|
Marcilla M, Cragnolini JJ, López de Castro JA. Proteasome-independent HLA-B27 ligands arise mainly from small basic proteins. Mol Cell Proteomics 2007; 6:923-38. [PMID: 17308301 DOI: 10.1074/mcp.m600302-mcp200] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Many of the constitutive peptide ligands of HLA-B27, a molecule strongly associated with spondyloarthritis, are proteasome-independent. Stable isotope tagging, mass spectrometry, and epoxomicin-mediated inhibition were used to determine their percentage, structural features, and parental proteins. Of 104 molecular species examined, 29.8% were proteasome-independent, paralleling the level of HLA-B27 re-expression in the presence of epoxomicin after acid stripping. Proteasome-dependent and -independent ligands differed little in peptide motifs, flanking sequences, and cellular localization of the parental proteins. In contrast, whereas the former set arose from proteins whose size and isoelectric point distribution largely reflected those in the human proteome, proteasome-independent ligands, other than a few matching signal sequences, were almost totally derived from small (about 6-16.5 kDa) and basic proteins, which account for only 6.6% of the human proteome. Thus, a non-proteasomal proteolytic pathway with strong preference for small proteins is responsible for a significant fraction of the HLA-B27-bound peptide repertoire.
Collapse
Affiliation(s)
- Miguel Marcilla
- Centro de Biología Molecular Severo Ochoa (Consejo Superior de Investigaciones Científicas and Universidad Autónoma de Madrid), Facultad de Ciencias, Universidad Autónoma, 28049 Madrid, Spain
| | | | | |
Collapse
|
47
|
Papadopoulos M, Momburg F. Multiple residues in the transmembrane helix and connecting peptide of mouse tapasin stabilize the transporter associated with the antigen-processing TAP2 subunit. J Biol Chem 2007; 282:9401-9410. [PMID: 17244610 DOI: 10.1074/jbc.m610429200] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The type I endoplasmic reticulum (ER) glycoprotein tapasin (Tpn) is essential for loading of major histocompatibility complex class I (MHC-I) molecules with an optimal spectrum of antigenic peptides and for stable expression of the heterodimeric, polytopic TAP peptide transporter. In a detailed mutational analysis, the transmembrane domain (TMD) and ER-luminal connecting peptide (CP) of mouse Tpn were analyzed for their capacity to stabilize the TAP2 subunit. Replacement of the TMD of Tpn by TMDs from calnexin or the Tpn-related protein, respectively, completely abolished TAP2 stabilization after transfection of Tpn-deficient cells, whereas TMDs derived from distantly related Tpn molecules (chicken and fish) were functional. A detailed mutational analysis of the TMD and adjacent residues in the ER-luminal CP of mouse Tpn was performed to elucidate amino acids that control the stabilization of TAP2. Single amino acid substitutions, including a conserved Lys residue in the center of the putative TMD, did not affect TAP2 expression levels. Mutation of this Lys plus four additional residues, predicted to be neighbors in an assumed alpha-helical TMD arrangement, abrogated the TAP2-stabilizing capacity of Tpn. In the presence of a wild-type TMD, also the substitution of a highly conserved Glu residue in the CP of Tpn strongly affected TAP2 stabilization. Defective TAP2 stabilization resulted in impaired cell surface expression of MHC-I molecules. This study thus defines a novel, spatially arranged motif in the TMD of Tpn essential for stable expression of the TAP2 protein and a novel protein interaction mode involving an ER-luminal Glu residue close to the membrane.
Collapse
Affiliation(s)
- Martina Papadopoulos
- Department of Molecular Immunology, German Cancer Research Center (DKFZ), 69120 Heidelberg, Germany
| | - Frank Momburg
- Department of Molecular Immunology, German Cancer Research Center (DKFZ), 69120 Heidelberg, Germany.
| |
Collapse
|
48
|
Koch J, Guntrum R, Tampé R. The first N-terminal transmembrane helix of each subunit of the antigenic peptide transporter TAP is essential for independent tapasin binding. FEBS Lett 2006; 580:4091-6. [PMID: 16828748 DOI: 10.1016/j.febslet.2006.06.053] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2006] [Revised: 05/30/2006] [Accepted: 06/16/2006] [Indexed: 01/06/2023]
Abstract
The heterodimeric ABC transporter TAP translocates proteasomal degradation products from the cytosol into the lumen of the endoplasmic reticulum, where these peptides are loaded onto MHC class I molecules by a macromolecular peptide-loading complex (PLC) and subsequently shuttled to the cell surface for inspection by cytotoxic T lymphocytes. Tapasin recruits, as a central adapter protein, other components of the PLC at the unique N-terminal domains of TAP. We found that the N-terminal domains of human TAP1 and TAP2 can independently bind to tapasin, thus providing two separate loading platforms for PLC assembly. Moreover, tapasin binding is dependent on the first N-terminal transmembrane helix of TAP1 and TAP2, demonstrating that these two helices contribute independently to the recruitment of tapasin and associated factors.
Collapse
Affiliation(s)
- Joachim Koch
- Institute of Biochemistry, Biocenter, Johann Wolfgang Goethe-University Frankfurt, Marie-Curie Strasse 9, D-69439 Frankfurt a.M., Germany.
| | | | | |
Collapse
|
49
|
Keusekotten K, Leonhardt RM, Ehses S, Knittler MR. Biogenesis of functional antigenic peptide transporter TAP requires assembly of pre-existing TAP1 with newly synthesized TAP2. J Biol Chem 2006; 281:17545-51. [PMID: 16624807 DOI: 10.1074/jbc.m602360200] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
The transporter associated with antigen processing (TAP) is essential for the delivery of antigenic peptides from the cytosol into the endoplasmic reticulum (ER), where they are loaded onto major histocompatibility complex class I molecules. TAP is a heterodimeric transmembrane protein that comprises the homologous subunits TAP1 and TAP2. As for many other oligomeric protein complexes, which are synthesized in the ER, the process of subunit assembly is essential for TAP to attain a native functional state. Here, we have analyzed the individual requirements of TAP1 and TAP2 for the formation of a functional TAP complex. Unlike TAP1, TAP2 is very unstable when expressed in isolation. We show that heterodimerization of TAP subunits is required for maintaining a stable level of TAP2. By using an in vitro expression system we demonstrate that the biogenesis of functional TAP depends on the assembly of preexisting TAP1 with newly synthesized TAP2, but not vice versa. The pore forming core transmembrane domain (core TMD) of in vitro expressed TAP2 is necessary and sufficient to allow functional complex formation with pre-existing TAP1. We propose that the observed assembly mechanism of TAP protects newly synthesized TAP2 from rapid degradation and controls the number of transport active transporter molecules. Our findings open up new possibilities to investigate functional and structural properties of TAP and provide a powerful model system to address the biosynthetic assembly of oligomeric transmembrane proteins in the ER.
Collapse
Affiliation(s)
- Kirstin Keusekotten
- Institute for Genetics, University of Cologne, Zuelpicher Strasse 47, D-50674 Cologne, Germany
| | | | | | | |
Collapse
|
50
|
Biemans-Oldehinkel E, Doeven MK, Poolman B. ABC transporter architecture and regulatory roles of accessory domains. FEBS Lett 2005; 580:1023-35. [PMID: 16375896 DOI: 10.1016/j.febslet.2005.11.079] [Citation(s) in RCA: 174] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2005] [Revised: 11/30/2005] [Accepted: 11/30/2005] [Indexed: 10/25/2022]
Abstract
We present an overview of the architecture of ATP-binding cassette (ABC) transporters and dissect the systems in core and accessory domains. The ABC transporter core is formed by the transmembrane domains (TMDs) and the nucleotide binding domains (NBDs) that constitute the actual translocator. The accessory domains include the substrate-binding proteins, that function as high affinity receptors in ABC type uptake systems, and regulatory or catalytic domains that can be fused to either the TMDs or NBDs. The regulatory domains add unique functions to the transporters allowing the systems to act as channel conductance regulators, osmosensors/regulators, and assemble into macromolecular complexes with specific properties.
Collapse
Affiliation(s)
- Esther Biemans-Oldehinkel
- Department of Biochemistry, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands
| | | | | |
Collapse
|