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- PDB-9rcv: Structure of the Human Peptide-Loading Complex Arrested by HCMV US6 -

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Entry
Database: PDB / ID: 9rcv
TitleStructure of the Human Peptide-Loading Complex Arrested by HCMV US6
Components
  • (Antigen peptide transporter ...) x 2
  • Beta-2-microglobulin
  • MHC class I antigen
  • Tapasin
  • Unique short US6 glycoprotein
KeywordsIMMUNE SYSTEM / antigen processing / adaptive immunity / cryo-EM / ER chaperones / MHC class I / transporter associated with antigen processing
Function / homology
Function and homology information


MHC class Ib protein complex assembly / peptide antigen stabilization / MHC class I protein complex binding / antigen processing and presentation of endogenous peptide antigen via MHC class Ib via ER pathway, TAP-dependent / tapasin binding / ABC-type peptide antigen transporter activity / ABC-type antigen peptide transporter / TAP complex / ABC-type peptide transporter activity / MHC class Ib protein binding ...MHC class Ib protein complex assembly / peptide antigen stabilization / MHC class I protein complex binding / antigen processing and presentation of endogenous peptide antigen via MHC class Ib via ER pathway, TAP-dependent / tapasin binding / ABC-type peptide antigen transporter activity / ABC-type antigen peptide transporter / TAP complex / ABC-type peptide transporter activity / MHC class Ib protein binding / peptide antigen transport / cytosol to endoplasmic reticulum transport / symbiont-mediated suppression of host antigen processing and presentation of peptide antigen via MHC class I / regulation of protein complex stability / TAP2 binding / TAP1 binding / peptide transport / peptide transmembrane transporter activity / TAP complex binding / retrograde vesicle-mediated transport, Golgi to endoplasmic reticulum / MHC class I protein binding / molecular sequestering activity / antigen processing and presentation of peptide antigen via MHC class I / endoplasmic reticulum-Golgi intermediate compartment membrane / protein folding chaperone / early endosome lumen / Nef mediated downregulation of MHC class I complex cell surface expression / DAP12 interactions / T cell mediated cytotoxicity / Endosomal/Vacuolar pathway / Antigen Presentation: Folding, assembly and peptide loading of class I MHC / lumenal side of endoplasmic reticulum membrane / antigen processing and presentation of exogenous protein antigen via MHC class Ib, TAP-dependent / regulation of iron ion transport / cellular response to iron(III) ion / negative regulation of iron ion transport / negative regulation of forebrain neuron differentiation / response to molecule of bacterial origin / regulation of erythrocyte differentiation / peptide antigen assembly with MHC class I protein complex / ER to Golgi transport vesicle membrane / defense response / HFE-transferrin receptor complex / MHC class I peptide loading complex / transferrin transport / negative regulation of receptor-mediated endocytosis / cellular response to iron ion / positive regulation of T cell cytokine production / multicellular organismal-level iron ion homeostasis / antigen processing and presentation of endogenous peptide antigen via MHC class I / MHC class I protein complex / ADP binding / peptide antigen assembly with MHC class II protein complex / positive regulation of T cell mediated cytotoxicity / negative regulation of epithelial cell proliferation / cellular response to nicotine / MHC class II protein complex / positive regulation of receptor-mediated endocytosis / negative regulation of neurogenesis / specific granule lumen / antigen processing and presentation of exogenous peptide antigen via MHC class II / positive regulation of immune response / peptide antigen binding / recycling endosome membrane / phagocytic vesicle membrane / positive regulation of T cell activation / Interferon gamma signaling / Immunoregulatory interactions between a Lymphoid and a non-Lymphoid cell / transmembrane transport / T cell differentiation in thymus / sensory perception of smell / Modulation by Mtb of host immune system / : / tertiary granule lumen / positive regulation of cellular senescence / MHC class II protein complex binding / DAP12 signaling / negative regulation of neuron projection development / late endosome membrane / protein transport / regulation of gene expression / protein refolding / ER-Phagosome pathway / protein-containing complex assembly / early endosome membrane / amyloid fibril formation / molecular adaptor activity / protein homotetramerization / adaptive immune response / intracellular iron ion homeostasis / learning or memory / immune response / host cell endoplasmic reticulum membrane / endoplasmic reticulum lumen / Amyloid fiber formation / external side of plasma membrane / Golgi membrane / lysosomal membrane / focal adhesion / Neutrophil degranulation
Similarity search - Function
Viral unique short region 6 / Viral unique short region 6 / Tapasin / Antigen peptide transporter 2 / ABC transporter Tap-like / Type 1 protein exporter / : / MHC class I, alpha chain, C-terminal / MHC_I C-terminus / ABC transporter transmembrane region ...Viral unique short region 6 / Viral unique short region 6 / Tapasin / Antigen peptide transporter 2 / ABC transporter Tap-like / Type 1 protein exporter / : / MHC class I, alpha chain, C-terminal / MHC_I C-terminus / ABC transporter transmembrane region / ABC transporter type 1, transmembrane domain / ABC transporter integral membrane type-1 fused domain profile. / ABC transporter type 1, transmembrane domain superfamily / MHC class I alpha chain, alpha1 alpha2 domains / Class I Histocompatibility antigen, domains alpha 1 and 2 / Beta-2-Microglobulin / : / MHC class I-like antigen recognition-like / MHC class I-like antigen recognition-like superfamily / ABC transporter-like, conserved site / ABC transporters family signature. / MHC classes I/II-like antigen recognition protein / : / ABC transporter / ABC transporter-like, ATP-binding domain / ATP-binding cassette, ABC transporter-type domain profile. / Immunoglobulin/major histocompatibility complex, conserved site / Immunoglobulins and major histocompatibility complex proteins signature. / Immunoglobulin C-Type / Immunoglobulin C1-set / Immunoglobulin C1-set domain / Ig-like domain profile. / Immunoglobulin-like domain / Immunoglobulin-like domain superfamily / ATPases associated with a variety of cellular activities / AAA+ ATPase domain / Immunoglobulin-like fold / P-loop containing nucleoside triphosphate hydrolase
Similarity search - Domain/homology
ADENOSINE-5'-DIPHOSPHATE / ADENOSINE-5'-TRIPHOSPHATE / MHC class I antigen / Tapasin / Unique short US6 glycoprotein / Beta-2-microglobulin / Antigen peptide transporter 1 / Antigen peptide transporter 2
Similarity search - Component
Biological speciesHomo sapiens (human)
MethodELECTRON MICROSCOPY / single particle reconstruction / cryo EM / Resolution: 2.7 Å
AuthorsStolz, M. / Susac, L. / Trowitzsch, S. / Tampe, R.
Funding supportEuropean Union, Germany, United States, 5items
OrganizationGrant numberCountry
European Research Council (ERC)789121European Union
European Research Council (ERC)101141396European Union
German Research Foundation (DFG)TA157/12-1 Germany
German Research Foundation (DFG)CRC1507/P18 Germany
Other privateUR013222 United States
Citation
Journal: Sci Adv / Year: 2026
Title: Architectural principles of transporter-chaperone coupling within the native MHC I peptide-loading complex.
Authors: Milena Stolz / Lukas Sušac / Amin Fahim / Rieke Keller / Lisa Saggau / Filippo Mancia / Simon Trowitzsch / Robert Tampé /
Abstract: Adaptive immunity depends on major histocompatibility complex class I (MHC I) presentation of peptides, a process orchestrated by the peptide-loading complex (PLC) in the endoplasmic reticulum (ER). ...Adaptive immunity depends on major histocompatibility complex class I (MHC I) presentation of peptides, a process orchestrated by the peptide-loading complex (PLC) in the endoplasmic reticulum (ER). The PLC ensures precise peptide selection and loading and is a major target of viral immune evasion, notably by human cytomegalovirus (HCMV). Here, we report the 2.59- to 2.88-Å cryo-electron microscopy structure of native human PLC bound to the HCMV immune evasin US6. US6 inhibits the transporter associated with antigen processing 1/2 (TAP1/2) by laterally attaching its transmembrane helix to TAP2 using a disulfide-rich domain to mimic a translocating peptide. This domain blocks the ER-lumenal exit and locks TAP in an outward-facing conformation with closed nucleotide-binding domains and asymmetric adenosine 5'-triphosphate/adenosine 5'-diphosphate occlusion. The structure also reveals how TAP's amino-terminal transmembrane domains scaffold the MHC I chaperone tapasin. These findings elucidate the mechanism of US6-mediated immune evasion and highlight potential targets for therapeutic modulation of immune presentation in infection and cancer.
#1: Journal: Acta Crystallogr D Struct Biol / Year: 2019
Title: Macromolecular structure determination using X-rays, neutrons and electrons: recent developments in Phenix.
Authors: Dorothee Liebschner / Pavel V Afonine / Matthew L Baker / Gábor Bunkóczi / Vincent B Chen / Tristan I Croll / Bradley Hintze / Li Wei Hung / Swati Jain / Airlie J McCoy / Nigel W Moriarty ...Authors: Dorothee Liebschner / Pavel V Afonine / Matthew L Baker / Gábor Bunkóczi / Vincent B Chen / Tristan I Croll / Bradley Hintze / Li Wei Hung / Swati Jain / Airlie J McCoy / Nigel W Moriarty / Robert D Oeffner / Billy K Poon / Michael G Prisant / Randy J Read / Jane S Richardson / David C Richardson / Massimo D Sammito / Oleg V Sobolev / Duncan H Stockwell / Thomas C Terwilliger / Alexandre G Urzhumtsev / Lizbeth L Videau / Christopher J Williams / Paul D Adams /
Abstract: Diffraction (X-ray, neutron and electron) and electron cryo-microscopy are powerful methods to determine three-dimensional macromolecular structures, which are required to understand biological ...Diffraction (X-ray, neutron and electron) and electron cryo-microscopy are powerful methods to determine three-dimensional macromolecular structures, which are required to understand biological processes and to develop new therapeutics against diseases. The overall structure-solution workflow is similar for these techniques, but nuances exist because the properties of the reduced experimental data are different. Software tools for structure determination should therefore be tailored for each method. Phenix is a comprehensive software package for macromolecular structure determination that handles data from any of these techniques. Tasks performed with Phenix include data-quality assessment, map improvement, model building, the validation/rebuilding/refinement cycle and deposition. Each tool caters to the type of experimental data. The design of Phenix emphasizes the automation of procedures, where possible, to minimize repetitive and time-consuming manual tasks, while default parameters are chosen to encourage best practice. A graphical user interface provides access to many command-line features of Phenix and streamlines the transition between programs, project tracking and re-running of previous tasks.
History
DepositionMay 29, 2025Deposition site: PDBE / Processing site: PDBE
Revision 1.0Dec 3, 2025Provider: repository / Type: Initial release
Revision 1.0Dec 3, 2025Data content type: EM metadata / Data content type: EM metadata / Provider: repository / Type: Initial release
Revision 1.0Dec 3, 2025Data content type: Image / Data content type: Image / Provider: repository / Type: Initial release
Revision 1.0Dec 3, 2025Data content type: Primary map / Data content type: Primary map / Provider: repository / Type: Initial release
Revision 1.1Feb 11, 2026Group: Data collection / Database references / Category: citation / citation_author / em_admin
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Revision 1.1Feb 11, 2026Data content type: EM metadata / Data content type: EM metadata / EM metadata / Group: Database references / Experimental summary / Data content type: EM metadata / EM metadata / EM metadata / Category: citation / citation_author / em_admin
Data content type: EM metadata / EM metadata ...EM metadata / EM metadata / EM metadata / EM metadata / EM metadata / EM metadata / EM metadata / EM metadata / EM metadata / EM metadata / EM metadata / EM metadata
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Revision 1.2Apr 15, 2026Group: Data collection / Category: em_admin / Item: _em_admin.last_update
Revision 1.2Apr 15, 2026Data content type: EM metadata / Data content type: EM metadata / Group: Experimental summary / Data content type: EM metadata / Category: em_admin / Data content type: EM metadata / Item: _em_admin.last_update

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Structure visualization

Structure viewerMolecule:
MolmilJmol/JSmol

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Assembly

Deposited unit
A: Antigen peptide transporter 1
B: Tapasin
C: MHC class I antigen
D: Beta-2-microglobulin
E: Antigen peptide transporter 2
F: Tapasin
G: MHC class I antigen
H: Beta-2-microglobulin
I: Unique short US6 glycoprotein
hetero molecules


Theoretical massNumber of molelcules
Total (without water)382,49717
Polymers380,2239
Non-polymers2,2748
Water724
1


  • Idetical with deposited unit
  • defined by author&software
  • Evidence: electron microscopy, not applicable, gel filtration
TypeNameSymmetry operationNumber
identity operation1_555x,y,z1

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Components

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Antigen peptide transporter ... , 2 types, 2 molecules AE

#1: Protein Antigen peptide transporter 1 / APT1 / ATP-binding cassette sub-family B member 2 / Peptide supply factor 1 / Peptide transporter ...APT1 / ATP-binding cassette sub-family B member 2 / Peptide supply factor 1 / Peptide transporter PSF1 / PSF-1 / Peptide transporter TAP1 / Peptide transporter involved in antigen processing 1 / Really interesting new gene 4 protein / RING4


Mass: 81080.383 Da / Num. of mol.: 1 / Source method: isolated from a natural source / Source: (natural) Homo sapiens (human) / Cell line: Raji / Tissue: Burkitt lymphoma
References: UniProt: Q03518, ABC-type antigen peptide transporter
#5: Protein Antigen peptide transporter 2 / APT2 / ATP-binding cassette sub-family B member 3 / Peptide supply factor 2 / Peptide transporter ...APT2 / ATP-binding cassette sub-family B member 3 / Peptide supply factor 2 / Peptide transporter PSF2 / PSF-2 / Peptide transporter TAP2 / Peptide transporter involved in antigen processing 2 / Really interesting new gene 11 protein / RING11


Mass: 74697.242 Da / Num. of mol.: 1 / Source method: isolated from a natural source / Source: (natural) Homo sapiens (human) / Cell line: Raji / Tissue: Burkitt lymphoma
References: UniProt: Q03519, ABC-type antigen peptide transporter

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Protein , 4 types, 7 molecules BFCGDHI

#2: Protein Tapasin / TPN / TPSN / NGS-17 / TAP-associated protein / TAP-binding protein


Mass: 47673.539 Da / Num. of mol.: 2 / Source method: isolated from a natural source / Source: (natural) Homo sapiens (human) / Cell line: Raji / Tissue: Burkitt lymphoma / References: UniProt: O15533
#3: Protein MHC class I antigen


Mass: 40480.973 Da / Num. of mol.: 2 / Source method: isolated from a natural source / Details: HLA-B*15:10 / Source: (natural) Homo sapiens (human) / Cell line: Raji / Tissue: Burkitt lymphoma / References: UniProt: A0A678ZHF8
#4: Protein Beta-2-microglobulin


Mass: 13732.547 Da / Num. of mol.: 2 / Source method: isolated from a natural source / Source: (natural) Homo sapiens (human) / Cell line: Raji / Tissue: Burkitt lymphoma / References: UniProt: P61769
#6: Protein Unique short US6 glycoprotein / Protein HXLF6 / gpUS6


Mass: 20671.127 Da / Num. of mol.: 1
Source method: isolated from a genetically manipulated source
Source: (gene. exp.) Homo sapiens (human) / Gene: US6 / Production host: Homo sapiens (human) / References: UniProt: P14334

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Sugars , 2 types, 4 molecules

#7: Polysaccharide 2-acetamido-2-deoxy-beta-D-glucopyranose-(1-4)-2-acetamido-2-deoxy-beta-D-glucopyranose


Type: oligosaccharide / Mass: 424.401 Da / Num. of mol.: 2
Source method: isolated from a genetically manipulated source
DescriptorTypeProgram
DGlcpNAcb1-4DGlcpNAcb1-ROHGlycam Condensed SequenceGMML 1.0
WURCS=2.0/1,2,1/[a2122h-1b_1-5_2*NCC/3=O]/1-1/a4-b1WURCSPDB2Glycan 1.1.0
[][D-1-deoxy-GlcpNAc]{[(4+1)][b-D-GlcpNAc]{}}LINUCSPDB-CARE
#10: Sugar ChemComp-NAG / 2-acetamido-2-deoxy-beta-D-glucopyranose / N-acetyl-beta-D-glucosamine / 2-acetamido-2-deoxy-beta-D-glucose / 2-acetamido-2-deoxy-D-glucose / 2-acetamido-2-deoxy-glucose / N-ACETYL-D-GLUCOSAMINE


Type: D-saccharide, beta linking / Mass: 221.208 Da / Num. of mol.: 2 / Source method: obtained synthetically / Formula: C8H15NO6 / Feature type: SUBJECT OF INVESTIGATION
IdentifierTypeProgram
DGlcpNAcbCONDENSED IUPAC CARBOHYDRATE SYMBOLGMML 1.0
N-acetyl-b-D-glucopyranosamineCOMMON NAMEGMML 1.0
b-D-GlcpNAcIUPAC CARBOHYDRATE SYMBOLPDB-CARE 1.0
GlcNAcSNFG CARBOHYDRATE SYMBOLGMML 1.0

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Non-polymers , 4 types, 8 molecules

#8: Chemical ChemComp-ATP / ADENOSINE-5'-TRIPHOSPHATE


Mass: 507.181 Da / Num. of mol.: 1 / Source method: obtained synthetically / Formula: C10H16N5O13P3 / Feature type: SUBJECT OF INVESTIGATION / Comment: ATP, energy-carrying molecule*YM
#9: Chemical ChemComp-MG / MAGNESIUM ION


Mass: 24.305 Da / Num. of mol.: 2 / Source method: obtained synthetically / Formula: Mg / Feature type: SUBJECT OF INVESTIGATION
#11: Chemical ChemComp-ADP / ADENOSINE-5'-DIPHOSPHATE


Mass: 427.201 Da / Num. of mol.: 1 / Source method: obtained synthetically / Formula: C10H15N5O10P2 / Feature type: SUBJECT OF INVESTIGATION / Comment: ADP, energy-carrying molecule*YM
#12: Water ChemComp-HOH / water


Mass: 18.015 Da / Num. of mol.: 4 / Source method: isolated from a natural source / Formula: H2O

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Details

Has ligand of interestY
Has protein modificationY

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Experimental details

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Experiment

ExperimentMethod: ELECTRON MICROSCOPY
EM experimentAggregation state: PARTICLE / 3D reconstruction method: single particle reconstruction

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Sample preparation

ComponentName: Human peptide-loading complex arrested by HCMV US6 / Type: COMPLEX / Entity ID: #1-#6 / Source: NATURAL
Molecular weight
IDEntity assembly-IDValue (°)Experimental value
110.570 MDaYES
21NO
Source (natural)Organism: Homo sapiens (human)
Buffer solutionpH: 6.5
Details: 20 mM HEPES-NaOH pH 6.5, 150 mM NaCl, 10 mM MgCl2, 2.5 mM biotin, 0.05% (w/v) glycodiosgenin
Buffer component
IDConc.NameFormulaBuffer-ID
120 mMHEPES-sodium hydroxideC8H18N2O4S-NaOH1
2150 mMsodium chlorideNaCl1
310 mMmagnesium chlorideMgCl21
40.05 %glycodiosgeninC56H92O251
52.5 mMbiotinC10H16N2O3S1
SpecimenConc.: 3.5 mg/ml / Embedding applied: NO / Shadowing applied: NO / Staining applied: NO / Vitrification applied: YES
Specimen supportGrid material: GOLD / Grid mesh size: 300 divisions/in. / Grid type: UltrAuFoil
VitrificationInstrument: FEI VITROBOT MARK IV / Cryogen name: ETHANE / Humidity: 100 % / Chamber temperature: 277 K / Details: Blot force 5, Blot time 5 s

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Electron microscopy imaging

Experimental equipment
Model: Titan Krios / Image courtesy: FEI Company
MicroscopyModel: TFS KRIOS
Electron gunElectron source: FIELD EMISSION GUN / Accelerating voltage: 300 kV / Illumination mode: FLOOD BEAM
Electron lensMode: BRIGHT FIELD / Nominal magnification: 105000 X / Calibrated magnification: 60241 X / Nominal defocus max: 1500 nm / Nominal defocus min: 500 nm / Cs: 2.7 mm
Specimen holderCryogen: NITROGEN / Specimen holder model: FEI TITAN KRIOS AUTOGRID HOLDER
Image recordingElectron dose: 58 e/Å2 / Film or detector model: GATAN K3 (6k x 4k) / Num. of grids imaged: 3 / Num. of real images: 25454

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Processing

EM softwareName: PHENIX / Category: model refinement
CTF correctionType: PHASE FLIPPING AND AMPLITUDE CORRECTION
Particle selectionNum. of particles selected: 726723
SymmetryPoint symmetry: C1 (asymmetric)
3D reconstructionResolution: 2.7 Å / Resolution method: OTHER / Num. of particles: 269213
Details: Composite map generated from 4 focus maps ranging 2.59 - 2.88 A
Symmetry type: POINT
RefinementCross valid method: NONE

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