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- PDB-9fkn: Human monocarboxylate transporter 8 bound to thyroxine -

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Basic information

Entry
Database: PDB / ID: 9fkn
TitleHuman monocarboxylate transporter 8 bound to thyroxine
Components
  • ALFA-tag nanobody
  • Monocarboxylate transporter 8
KeywordsTRANSPORT PROTEIN / Thyroid / Hormones / SLC16A2 / Transporter / Thyroxine
Function / homology
Function and homology information


thyroid-stimulating hormone secretion / monocarboxylic acid transmembrane transporter activity / monocarboxylic acid transport / Organic anion transport by SLCO transporters / thyroid hormone metabolic process / negative regulation of neural precursor cell proliferation / thyroid hormone transmembrane transporter activity / thyroid hormone transport / amino acid import across plasma membrane / amino acid transmembrane transporter activity ...thyroid-stimulating hormone secretion / monocarboxylic acid transmembrane transporter activity / monocarboxylic acid transport / Organic anion transport by SLCO transporters / thyroid hormone metabolic process / negative regulation of neural precursor cell proliferation / thyroid hormone transmembrane transporter activity / thyroid hormone transport / amino acid import across plasma membrane / amino acid transmembrane transporter activity / thyroid hormone generation / amino acid metabolic process / transport across blood-brain barrier / apical plasma membrane / identical protein binding / plasma membrane
Similarity search - Function
: / Major facilitator superfamily / Major Facilitator Superfamily / Major facilitator superfamily domain / Major facilitator superfamily (MFS) profile. / MFS transporter superfamily
Similarity search - Domain/homology
3,5,3',5'-TETRAIODO-L-THYRONINE / Monocarboxylate transporter 8
Similarity search - Component
Biological speciesHomo sapiens (human)
Vicugna pacos (alpaca)
MethodELECTRON MICROSCOPY / single particle reconstruction / cryo EM / Resolution: 3.4 Å
AuthorsCoscia, F. / Tassinari, M.
Funding supportEuropean Union, 1items
OrganizationGrant numberCountry
European Research Council (ERC)101041298 THYROMOLEuropean Union
CitationJournal: Nat Commun / Year: 2025
Title: Molecular mechanism of thyroxine transport by monocarboxylate transporters.
Authors: Matteo Tassinari / Giorgia Tanzi / Francesco Maggiore / Stefan Groeneweg / Ferdy S van Geest / Matthijs E T Freund / Christiaan J Stavast / Irene Boniardi / Sebastiano Pasqualato / W Edward ...Authors: Matteo Tassinari / Giorgia Tanzi / Francesco Maggiore / Stefan Groeneweg / Ferdy S van Geest / Matthijs E T Freund / Christiaan J Stavast / Irene Boniardi / Sebastiano Pasqualato / W Edward Visser / Francesca Coscia /
Abstract: Thyroid hormones (the common name for prohormone thyroxine and the bioactive form triiodothyronine) control major developmental and metabolic processes. Release of thyroid hormones from the thyroid ...Thyroid hormones (the common name for prohormone thyroxine and the bioactive form triiodothyronine) control major developmental and metabolic processes. Release of thyroid hormones from the thyroid gland into the bloodstream and their transport into target cells is facilitated by plasma membrane transporters, including monocarboxylate transporter (MCT)8 and the highly homologous MCT10. However, the molecular mechanism underlying thyroid hormone transport is unknown. The relevance of such transporters is illustrated in patients with MCT8 deficiency, a severe neurodevelopmental and metabolic disorder. Using cryogenic-sample electron microscopy (cryo-EM), we determined the ligand-free and thyroxine-bound human MCT8 structures in the outward-facing state and the thyroxine-bound human MCT10 in the inward-facing state. Our structural analysis revealed a network of conserved gate residues involved in conformational changes upon thyroxine binding, triggering ligand release in the opposite compartment. We then determined the structure of a folded but inactive patient-derived MCT8 mutant, indicating a subtle conformational change which explains its reduced transport activity. Finally, we report a structure of MCT8 bound to its inhibitor silychristin, locked in the outward-facing state, revealing the molecular basis of its action and specificity. Taken together, this study advances mechanistic understanding of normal and disordered thyroid hormone transport.
History
DepositionJun 3, 2024Deposition site: PDBE / Processing site: PDBE
Revision 1.0May 21, 2025Provider: repository / Type: Initial release
Revision 1.0May 21, 2025Data content type: EM metadata / Data content type: EM metadata / Provider: repository / Type: Initial release
Revision 1.0May 21, 2025Data content type: FSC / Data content type: FSC / Provider: repository / Type: Initial release
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Revision 1.1Jun 11, 2025Group: Data collection / Database references / Category: citation / citation_author / em_admin
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Revision 1.1Jul 9, 2025Data content type: EM metadata / Data content type: EM metadata / EM metadata / Group: Data processing / Experimental summary / Data content type: EM metadata / EM metadata / Category: em_admin / em_software / Data content type: EM metadata / EM metadata / Item: _em_admin.last_update / _em_software.name

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Structure visualization

Structure viewerMolecule:
MolmilJmol/JSmol

Downloads & links

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Assembly

Deposited unit
A: Monocarboxylate transporter 8
B: ALFA-tag nanobody
hetero molecules


Theoretical massNumber of molelcules
Total (without water)72,1523
Polymers71,3752
Non-polymers7771
Water00
1


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

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Components

#1: Protein Monocarboxylate transporter 8 / MCT 8 / Monocarboxylate transporter 7 / MCT 7 / Solute carrier family 16 member 2 / X-linked PEST- ...MCT 8 / Monocarboxylate transporter 7 / MCT 7 / Solute carrier family 16 member 2 / X-linked PEST-containing transporter


Mass: 57775.887 Da / Num. of mol.: 1
Source method: isolated from a genetically manipulated source
Source: (gene. exp.) Homo sapiens (human) / Gene: SLC16A2, MCT7, MCT8, XPCT / Production host: Homo sapiens (human) / References: UniProt: P36021
#2: Antibody ALFA-tag nanobody


Mass: 13599.183 Da / Num. of mol.: 1
Source method: isolated from a genetically manipulated source
Details: Nanobody anti-ALFA tag as in the PDB 6I2G, with N-ter TEV cleavage site.
Source: (gene. exp.) Vicugna pacos (alpaca) / Gene: Synthetic construct / Production host: Escherichia coli BL21(DE3) (bacteria)
#3: Chemical ChemComp-T44 / 3,5,3',5'-TETRAIODO-L-THYRONINE


Mass: 776.870 Da / Num. of mol.: 1 / Source method: obtained synthetically / Formula: C15H11I4NO4 / Feature type: SUBJECT OF INVESTIGATION
Has ligand of interestY
Has protein modificationN

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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: ALFA-tag nanobody bound to MCT8 in complex to T4 / Type: COMPLEX / Entity ID: #1-#2 / Source: RECOMBINANT
Molecular weightValue: 0.071 MDa / Experimental value: NO
Source (natural)Organism: Homo sapiens (human)
Source (recombinant)Organism: Homo sapiens (human)
Buffer solutionpH: 7.5
Buffer component
IDConc.NameFormulaBuffer-ID
1150 mMsodium chlorideNaCl1
225 mMHEPES4-(2-hydroxyethyl)-1-piperazineethanesulfonic1
SpecimenConc.: 0.5 mg/ml / Embedding applied: NO / Shadowing applied: NO / Staining applied: NO / Vitrification applied: YES / Details: MCT8 stabilised in amphipols PMAL-C8
Specimen supportGrid material: COPPER / Grid mesh size: 300 divisions/in. / Grid type: Quantifoil R1.2/1.3
VitrificationInstrument: FEI VITROBOT MARK IV / Cryogen name: ETHANE / Humidity: 100 % / Chamber temperature: 279.15 K

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Electron microscopy imaging

Experimental equipment
Model: Titan Krios / Image courtesy: FEI Company
MicroscopyModel: FEI TITAN KRIOS
Electron gunElectron source: FIELD EMISSION GUN / Accelerating voltage: 300 kV / Illumination mode: FLOOD BEAM
Electron lensMode: BRIGHT FIELD / Nominal defocus max: 1800 nm / Nominal defocus min: 800 nm
Image recordingElectron dose: 70 e/Å2 / Film or detector model: FEI FALCON IV (4k x 4k) / Num. of grids imaged: 1 / Num. of real images: 22504

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Processing

EM software
IDNameVersionCategoryDetails
2EPUimage acquisition
8PHENIXmodel refinement
10cryoSPARCinitial Euler assignment
11RELION5final Euler assignmentBlush
CTF correctionType: NONE
3D reconstructionResolution: 3.4 Å / Resolution method: FSC 0.143 CUT-OFF / Num. of particles: 173884 / Symmetry type: POINT
Refine LS restraints
Refine-IDTypeDev idealNumber
ELECTRON MICROSCOPYf_bond_d0.0034050
ELECTRON MICROSCOPYf_angle_d0.4925484
ELECTRON MICROSCOPYf_dihedral_angle_d10.3131430
ELECTRON MICROSCOPYf_chiral_restr0.037614
ELECTRON MICROSCOPYf_plane_restr0.003687

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