Journal: Nat Commun / Year: 2018 Title: Cryo-EM structures of human STEAP4 reveal mechanism of iron(III) reduction. Authors: Wout Oosterheert / Laura S van Bezouwen / Remco N P Rodenburg / Joke Granneman / Friedrich Förster / Andrea Mattevi / Piet Gros / Abstract: Enzymes of the six-transmembrane epithelial antigen of the prostate (STEAP) family reduce Fe and Cu ions to facilitate metal-ion uptake by mammalian cells. STEAPs are highly upregulated in several ...Enzymes of the six-transmembrane epithelial antigen of the prostate (STEAP) family reduce Fe and Cu ions to facilitate metal-ion uptake by mammalian cells. STEAPs are highly upregulated in several types of cancer, making them potential therapeutic targets. However, the structural basis for STEAP-catalyzed electron transfer through an array of cofactors to metals at the membrane luminal side remains elusive. Here, we report cryo-electron microscopy structures of human STEAP4 in absence and presence of Fe-NTA. Domain-swapped, trimeric STEAP4 orients NADPH bound to a cytosolic domain onto axially aligned flavin-adenine dinucleotide (FAD) and a single b-type heme that cross the transmembrane-domain to enable electron transfer. Substrate binding within a positively charged ring indicates that iron gets reduced while in complex with its chelator. These molecular principles of iron reduction provide a basis for exploring STEAPs as therapeutic targets.
pH: 5.5 / Details: 25 mM MES pH 5.5 200 mM NaCl 0.08% digitonin (w/v)
Buffer component
ID
Conc.
Name
Formula
Buffer-ID
1
200mM
sodiumchloride
NaCl
1
2
25mM
2-(N-morpholino)ethanesulfonic acid
C6H13NO4S
1
3
0.08 % (w/v)
DIGITONIN
C56H92O29
1
Specimen
Conc.: 4 mg/ml / Embedding applied: NO / Shadowing applied: NO / Staining applied: NO / Vitrification applied: YES Details: human STEAP4 was purified from the HEK293 GNTI- cell membrane through Strep-affinity chromatography and size-exclusion chromatography (SEC). After SEC in digitonin, the sample was ...Details: human STEAP4 was purified from the HEK293 GNTI- cell membrane through Strep-affinity chromatography and size-exclusion chromatography (SEC). After SEC in digitonin, the sample was monodisperse. Cofactors NADPH and FAD were added before grid freezing.
Instrument: FEI VITROBOT MARK IV / Cryogen name: ETHANE / Humidity: 100 % / Chamber temperature: 293 K / Details: blot time 4seconds blot force 0
-
Electron microscopy imaging
Experimental equipment
Model: Talos Arctica / Image courtesy: FEI Company
Microscopy
Model: FEI TALOS ARCTICA Details: 200 kV Talos Arctica at Utrecht University, the Netherlands.
Electron gun
Electron source: FIELD EMISSION GUN / Accelerating voltage: 200 kV / Illumination mode: FLOOD BEAM
Electron lens
Mode: BRIGHT FIELD / Nominal magnification: 130000 X / Nominal defocus max: 3000 nm / Nominal defocus min: 800 nm / Cs: 2.7 mm / C2 aperture diameter: 50 µm / Alignment procedure: COMA FREE
Specimen holder
Cryogen: NITROGEN
Image recording
Average exposure time: 6 sec. / Electron dose: 45.5 e/Å2 / Detector mode: SUPER-RESOLUTION / Film or detector model: GATAN K2 SUMMIT (4k x 4k) / Num. of grids imaged: 1 / Num. of real images: 2321
EM imaging optics
Energyfilter slit width: 20 eV
Image scans
Width: 3838 / Height: 3710 / Movie frames/image: 24 / Used frames/image: 1-24
-
Processing
Software
Name
Version
Classification
NB
PHENIX
1.13rc1_2958
refinement
PHENIX
1.13rc1_2958
refinement
EM software
ID
Name
Version
Category
1
RELION
2.1b1
particleselection
2
EPU
imageacquisition
4
Gctf
1.06
CTFcorrection
10
RELION
2.1b1
initialEulerassignment
11
RELION
2.1b1
finalEulerassignment
12
RELION
2.1b1
classification
13
RELION
2.1b1
3Dreconstruction
CTF correction
Details: performed in GCTF. / Type: PHASE FLIPPING AND AMPLITUDE CORRECTION
Particle selection
Num. of particles selected: 421438 / Details: Autopicked in Relion.
Symmetry
Point symmetry: C3 (3 fold cyclic)
3D reconstruction
Resolution: 3.8 Å / Resolution method: FSC 0.143 CUT-OFF / Num. of particles: 209075 / Details: performed by RELION. / Num. of class averages: 1 / Symmetry type: POINT
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