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- EMDB-39891: Focused refinement map of human HCAR1-Gi complex without ligand (... -

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Basic information

Entry
Database: EMDB / ID: EMD-39891
TitleFocused refinement map of human HCAR1-Gi complex without ligand (apo state) composite map
Map data
Sample
  • Complex: Focused refinement map of human HCAR1-Gi complex without ligand (apo state) composite map
    • Protein or peptide: Hydroxycarboxylic acid receptor 1
    • Protein or peptide: Guanine nucleotide-binding protein G(i) subunit alpha-1
    • Protein or peptide: Guanine nucleotide-binding protein G(I)/G(S)/G(T) subunit beta-1
    • Protein or peptide: Guanine nucleotide-binding protein G(I)/G(S)/G(O) subunit gamma-2
Keywordshydroxycarboxylic acid receptor / Class A GPCR / MEMBRANE PROTEIN
Biological speciesHomo sapiens (human)
Methodsingle particle reconstruction / cryo EM / Resolution: 3.12 Å
AuthorsGao M / Zang S / Zhu Y / Mao C / Zhang Y / Ma X
Funding support1 items
OrganizationGrant numberCountry
Not funded
CitationJournal: Sci Signal / Year: 2026
Title: Structural insights into the activation mechanism of the human metabolite receptor HCAR1.
Authors: Mengru Gao / ShaoKun Zang / Yanqing Zhu / Kun Xi / Yage Du / Shizhuo Cheng / Luwei Miao / Yanhui Lu / Chunyou Mao / Yan Zhang / Xin Ma /
Abstract: Hydroxycarboxylic acid receptor 1 (HCAR1) is a class A G protein-coupled receptor (GPCR) that is activated by the endogenous metabolite l-lactate and that plays an important role in various metabolic ...Hydroxycarboxylic acid receptor 1 (HCAR1) is a class A G protein-coupled receptor (GPCR) that is activated by the endogenous metabolite l-lactate and that plays an important role in various metabolic and inflammatory disorders. HCAR1 uses distinct ligand recognition and self-activation mechanisms to mediate specific pathophysiological functions through Gα and β-arrestin signaling pathways. To support effective drug development targeting HCAR1, we investigated ligand recognition and activation mechanisms through cryo-electron microscopy (cryo-EM) structures of the HCAR1-Gα complex in the apo state or with l-lactate or with the synthetic agonist CHBA. Compared with other HCARs, HCAR1 has a more compact binding pocket, which is stabilized by three unique disulfide bonds. l-lactate exhibited a flexible binding mode and relatively weak intermolecular interactions, thus requiring millimolar concentrations for receptor activation. In contrast, the binding of CHBA was more stable because of its chlorinated benzene ring, thus resulting in improved agonist potency. Structural comparisons with HCAR2 identified critical residues that restrict the size of the binding pocket of HCAR1 and influence ligand selectivity. Self-activation of HCAR1 is driven by conformational rearrangements within extracellular loop 2, with Phe168 playing a pivotal role as the key agonist. Together, these results clarify the mechanisms underlying HCAR1 activation, self-activation, and ligand selectivity, providing a structural framework for the design of high-affinity, selective agonists and inverse agonists with minimized off-target effects.
History
DepositionApr 25, 2024-
Header (metadata) releaseOct 29, 2025-
Map releaseOct 29, 2025-
UpdateMay 13, 2026-
Current statusMay 13, 2026Processing site: PDBc / Status: Released

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Structure visualization

Supplemental images

emd_39891.png

Downloads & links

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Map

FileDownload / File: emd_39891.map.gz / Format: CCP4 / Size: 42.9 MB / Type: IMAGE STORED AS FLOATING POINT NUMBER (4 BYTES)
Projections & slices

Image control

Size
Brightness
Contrast
Others
AxesZ (Sec.)Y (Row.)X (Col.)
0.93 Å/pix.
x 224 pix.
= 208.32 Å		0.93 Å/pix.
x 224 pix.
= 208.32 Å		0.93 Å/pix.
x 224 pix.
= 208.32 Å

Surface

Projections

Slices (1/3)

Slices (1/2)

Slices (2/3)

Images are generated by Spider.

Voxel sizeX=Y=Z: 0.93 Å
Density

Histogram

Histogram (log scale)
Contour LevelBy AUTHOR: 0.19
Minimum - Maximum-1.6876484 - 2.441276
Average (Standard dev.)0.0006016743 (±0.033672597)
SymmetrySpace group: 1
Details

EMDB XML:

Map geometry
Axis orderXYZ
Origin000
Dimensions224224224
Spacing224224224
CellA=B=C: 208.32 Å
α=β=γ: 90.0 °

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Supplemental data

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Half map: #1

Fileemd_39891_half_map_1.map
Projections & Slices
AxesZYX

Projections

Slices (1/2)
Density Histograms

Histogram

Histogram (log scale)

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Half map: #2

Fileemd_39891_half_map_2.map
Projections & Slices
AxesZYX

Projections

Slices (1/2)
Density Histograms

Histogram

Histogram (log scale)

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Sample components

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Entire : Focused refinement map of human HCAR1-Gi complex without ligand (...

EntireName: Focused refinement map of human HCAR1-Gi complex without ligand (apo state) composite map
Components
  • Complex: Focused refinement map of human HCAR1-Gi complex without ligand (apo state) composite map
    • Protein or peptide: Hydroxycarboxylic acid receptor 1
    • Protein or peptide: Guanine nucleotide-binding protein G(i) subunit alpha-1
    • Protein or peptide: Guanine nucleotide-binding protein G(I)/G(S)/G(T) subunit beta-1
    • Protein or peptide: Guanine nucleotide-binding protein G(I)/G(S)/G(O) subunit gamma-2

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Supramolecule #1: Focused refinement map of human HCAR1-Gi complex without ligand (...

SupramoleculeName: Focused refinement map of human HCAR1-Gi complex without ligand (apo state) composite map
type: complex / ID: 1 / Parent: 0 / Macromolecule list: all
Source (natural)Organism: Homo sapiens (human)

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Macromolecule #1: Hydroxycarboxylic acid receptor 1

MacromoleculeName: Hydroxycarboxylic acid receptor 1 / type: protein_or_peptide / ID: 1 / Enantiomer: LEVO
Source (natural)Organism: Homo sapiens (human)
Recombinant expressionOrganism: Spodoptera frugiperda (fall armyworm)
SequenceString: MYNGSCCRIE GDTISQVMPP LLIVAFVLGA LGNGVALCGF CFHMKTWKPS TVYLFNLAVA DFLLMICLPF RTDYYLRRRH WAFGDIPCR VGLFTLAMNR AGSIVFLTVV AADRYFKVVH PHHAVNTIST RVAAGIVCTL WALVILGTVY LLLENHLCVQ E TAVSCESF ...String:
MYNGSCCRIE GDTISQVMPP LLIVAFVLGA LGNGVALCGF CFHMKTWKPS TVYLFNLAVA DFLLMICLPF RTDYYLRRRH WAFGDIPCR VGLFTLAMNR AGSIVFLTVV AADRYFKVVH PHHAVNTIST RVAAGIVCTL WALVILGTVY LLLENHLCVQ E TAVSCESF IMESANGWHD IMFQLEFFMP LGIILFCSFK IVWSLRRRQQ LARQARMKKA TRFIMVVAIV FITCYLPSVS AR LYFLWTV PSSACDPSVH GALHITLSFT YMNSMLDPLV YYFSSPSFPK FYNKLKICSL KPKQPGHSKT QRPEEMPISN LGR RSCISV ANSFQSQSDG QWDPHIVEWH

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Macromolecule #2: Guanine nucleotide-binding protein G(i) subunit alpha-1

MacromoleculeName: Guanine nucleotide-binding protein G(i) subunit alpha-1
type: protein_or_peptide / ID: 2 / Enantiomer: LEVO
Source (natural)Organism: Homo sapiens (human)
Recombinant expressionOrganism: Spodoptera frugiperda (fall armyworm)
SequenceString: MGCTLSAEDK AAVERSKMID RNLREDGEKA AREVKLLLLG AGESGKNTIV KQMKIIHEAG YSEEECKQYK AVVYSNTIQS IIAIIRAMG RLKIDFGDSA RADDARQLFV LAGAAEEGFM TAELAGVIKR LWKDSGVQAC FNRSREYQLN DSAAYYLNDL D RIAQPNYI ...String:
MGCTLSAEDK AAVERSKMID RNLREDGEKA AREVKLLLLG AGESGKNTIV KQMKIIHEAG YSEEECKQYK AVVYSNTIQS IIAIIRAMG RLKIDFGDSA RADDARQLFV LAGAAEEGFM TAELAGVIKR LWKDSGVQAC FNRSREYQLN DSAAYYLNDL D RIAQPNYI PTQQDVLRTR VKTTGIVETH FTFKDLHFKM FDVGAQRSER KKWIHCFEGV TAIIFCVALS DYDLVLAEDE EM NRMHASM KLFDSICNNK WFTDTSIILF LNKKDLFEEK IKKSPLTICY PEYAGSNTYE EAAAYIQCQF EDLNKRKDTK EIY THFTCS TDTKNVQFVF DAVTDVIIKN NLKDCGLF

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Macromolecule #3: Guanine nucleotide-binding protein G(I)/G(S)/G(T) subunit beta-1

MacromoleculeName: Guanine nucleotide-binding protein G(I)/G(S)/G(T) subunit beta-1
type: protein_or_peptide / ID: 3 / Enantiomer: LEVO
Source (natural)Organism: Homo sapiens (human)
Recombinant expressionOrganism: Spodoptera frugiperda (fall armyworm)
SequenceString: MGSLLQSELD QLRQEAEQLK NQIRDARKAC ADATLSQITN NIDPVGRIQM RTRRTLRGHL AKIYAMHWGT DSRLLVSASQ DGKLIIWDS YTTNKVHAIP LRSSWVMTCA YAPSGNYVAC GGLDNICSIY NLKTREGNVR VSRELAGHTG YLSCCRFLDD N QIVTSSGD ...String:
MGSLLQSELD QLRQEAEQLK NQIRDARKAC ADATLSQITN NIDPVGRIQM RTRRTLRGHL AKIYAMHWGT DSRLLVSASQ DGKLIIWDS YTTNKVHAIP LRSSWVMTCA YAPSGNYVAC GGLDNICSIY NLKTREGNVR VSRELAGHTG YLSCCRFLDD N QIVTSSGD TTCALWDIET GQQTTTFTGH TGDVMSLSLA PDTRLFVSGA CDASAKLWDV REGMCRQTFT GHESDINAIC FF PNGNAFA TGSDDATCRL FDLRADQELM TYSHDNIICG ITSVSFSKSG RLLLAGYDDF NCNVWDALKA DRAGVLAGHD NRV SCLGVT DDGMAVATGS WDSFLKIWN

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Macromolecule #4: Guanine nucleotide-binding protein G(I)/G(S)/G(O) subunit gamma-2

MacromoleculeName: Guanine nucleotide-binding protein G(I)/G(S)/G(O) subunit gamma-2
type: protein_or_peptide / ID: 4 / Enantiomer: LEVO
Source (natural)Organism: Homo sapiens (human)
Recombinant expressionOrganism: Spodoptera frugiperda (fall armyworm)
SequenceString:
ASNNTASIAQ ARKLVEQLKM EANIDRIKVS KAAADLMAYC EAHAKEDPLL TPVPASENPF REKKFFCAIL

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Experimental details

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Structure determination

Methodcryo EM
Processingsingle particle reconstruction
Aggregation stateparticle

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Sample preparation

Concentration15 mg/mL
BufferpH: 7.5
VitrificationCryogen name: ETHANE

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Electron microscopy

MicroscopeTFS KRIOS
Image recordingFilm or detector model: FEI FALCON IV (4k x 4k) / Average electron dose: 52.0 e/Å2
Electron beamAcceleration voltage: 300 kV / Electron source: FIELD EMISSION GUN
Electron opticsIllumination mode: FLOOD BEAM / Imaging mode: BRIGHT FIELD / Cs: 2.7 mm / Nominal defocus max: 2.0 µm / Nominal defocus min: 1.0 µm
Sample stageSpecimen holder model: FEI TITAN KRIOS AUTOGRID HOLDER / Cooling holder cryogen: NITROGEN
Experimental equipment
Model: Titan Krios / Image courtesy: FEI Company

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Image processing

CTF correctionType: PHASE FLIPPING AND AMPLITUDE CORRECTION
Startup modelType of model: NONE
Final reconstructionResolution.type: BY AUTHOR / Resolution: 3.12 Å / Resolution method: FSC 0.143 CUT-OFF / Number images used: 252930
Initial angle assignmentType: RANDOM ASSIGNMENT
Final angle assignmentType: MAXIMUM LIKELIHOOD

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