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Biochemistry 9001
“Protein structure determination by 3D Electron Microscopy”
Tommi A. White, Ph.D.
Director, Electron Microscopy Core Facility
Assistant Research Professor, Biochemistry
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Goals of this course
• Introduce and familiarize you to concepts related to 3D Electron Microscopy and protein structure determination
• Provide hands on training and techniques to assist you in protein structure determination using electron microscopy
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Biochem 9001 alumni pursuing cryoEM:Bassem Shebl - 2015 Tara Marcink - 2017
Amadee des Georges, CUNYManhattan, New York
Tom Walz Lab, Rockefeller UniversityManhattan, New York
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Instructors
• Tommi A. White• Director, EMC & Research Asst Prof, Biochemistry
• Jacob Gotberg • Cyberinfrastructure Engineer, Research Computing Support
Services
• Filiz Bunyak• Research Asst Prof, Computer Science
TEACHING ASSISTANTS• Nguyen Phuoc Nguyen (“Wen”) – Computer Science
• Ashley Campbell - Biochemistry
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Course structure
• 8 lectures
• 5 labs & lab reports
• 3 weeks for individual projects• Project Abstract
• Project Presentation
• Project report
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Lectures
• Mondays/Wed: 10:30 am – noon, Vet Med W116• Theory, Literature review, examples from literature and
EMC
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Labs• 3 hours: in EMC, W125-W137 Veterinary Medicine
• Pairs (sign up!)• Tuesday/Thursday: 9-noon
• No labs 6/4-6/5
• Hands on applications, demonstration and Labs
• Register in “Facility Online Manager”• http://emc.missouri.edu/policies-info/
• http://emc.missouri.edu/reservations/
• Use MoCode F0146 (“zero”)
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• Hosted by Office of Research
• Early 90’s had electron microscopes in
– Geological Sciences
– CAFNR
– School of Medicine
– Veterinary medicine
• 1995 combined into Electron Microscopy
Core
– Hosted by Veterinary Pathology
– Located in Veterinary Medicine Building
Veterinar
y
Medicine
Building
Life
Sciences
Connawa
y
Stairs
Client
Sample
Preparation
Microtomy
Cryo Prep/
MechanicalMaterials
Prep
Staff
Office
JEOL
1400
TEM
EMC
Conference
room
FEI
Scios
FIBSEM
Staff
Specimen
Preparation
FEI
Tecnai
F30
TEM
FEI
Quanta 600
ESEM
Electron Microscopy Core (EMC)
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Projects
• before June 29th – Project consultation
• July 2nd– Project Abstract, 3 slides
• July 2-20 – Project Data Collection/Processing
• July 25th – Project Presentation, 30 min
• July 27th – Project Report, Microscopy & Microanalysis Paper format
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High Performance ComputationJacob Gotberg
• Generate ssh keys• http://docs.rnet.missouri.
edu/HowTo/ssh
• Share only your PUBLIC key, never share your private one
• Tutorials
• Nguyen Nguyen
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Why do we need 3D?
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Frank, 2006
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Williams & Carter, 1996
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What is 3DEM?
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What is 3DEM?• 3-Dimensional Electron Microscopy
• Using electron microscopy to determine a structure in 3-dimensions
• Cellular• Subcellular (organelles/membranes)• Proteins
• Proteins are embedded to maintain their shape• Heavy metal stain (negative staining)• Sugar (trehalose)• Ice (non-crystalline)
• Examples:• Single Particle Reconstruction (Single Particle Analysis, Cheng
Lab)• Random Conical Tilt (RCT, Radermacher Lab)• Electron Tomography (Subvolume Averaging, Subramaniam)• Electron Crystallography (MicroED, Gonen Lab)• Serial Block Face Imaging (FIBSEM Tomography, Denk Lab)
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Single Particle Reconstruction
Animations courtesy of Max Planck Institute of Biochemistry, Martinsried, Germany
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3DEM Examples: Single Particle Reconstruction
Ribosome structures to near-atomic (4.1 Å) resolution from thirty thousand cryo-EM particles (2013)Xiao-chen Bai, Israel S Fernandez, Greg McMullan, Sjors HW Scheres
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3DEM Examples: Single Particle Reconstruction
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Cryo-Electron Tomography
Animations courtesy of Max Planck Institute of Biochemistry, Martinsried, Germany
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3DEM Examples: Cryo-electron Tomography: SIV virions
T.A. White, A. Bartesaghi…S. Subramaniam (2011) PLoS Pathogens
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3DEM Examples: Cryo-electron Tomography: Chlamydomonas
B. Engel, M. Schaffer….W. Baumeister (2015) eLife
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3DEM Examples: Cryo-electron Tomography: Chlamydomonas
B. Engel, M. Schaffer….W. Baumeister (2015) eLife
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3DEM Examples: Cryo-electron Tomography: HeLa Cell
J. Mahamid…Baumeister, (2016) Science
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3DEM Examples: Serial Block Face imaging
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Nature’s Method of the Year 2015:
Cryo-EM
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NATURE | VOL 525 | 10 SEPTEMBER 2015
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Nobel Prize in Chemistry 2017 cryo-electron microscopy
Dubochet Frank Henderson
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Barrier
PSI-1PSI-2
$500 Mio
DNA sequencing XRC/NMR
5%
Structural Biology in the Post Genomics Era
1.000 Scientists in 40 countries
???
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Structures solved: XPC6/3/2018
Graph from the Protein Databank (PDB) June 2018
X-ray Protein Crystallography
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Structures solved: NMR
Nuclear Magnetic Resonance
Graph from the Protein Databank (PDB) June 2018
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Structures solved: CryoEM
Graph from the Protein Databank (PDB) June 2018
Cryo-electron Microscopy
DRAMATIC GROWTH of structures determined by CryoEM
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Comparison to X-ray Crystallography
• To determine the structure factors, need both
• amplitudes • phase
• “Phase problem”• In diffraction patterns, you can only
measure the intensity/amplitudes of the planes
• “Phase measuring diffractometer”- W. Hoppe, 1983
• With TEM images, we measure both amplitude and phase
Callaway (2015) Science
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Cryo-TEM is Unique
• protein complexes and molecular machines/assemblies
• molecular motions and dynamic processes
• heterogeneous samples
• no crystallization needed
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Proteins Act in Complexes6/3/2018
Cell (Vol. 122, No. 6, September 23, 2005, pp. 957-968).
• automated Yeast two-hybrid system• 3186 mostly novel protein interactions
among 1705 proteins• large highly connected network• resulted in 911 high-confidence
interactions among 401 proteins
A Human Protein-Protein Interaction Network
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Added Value of Cryo-TEM
35
1 32 54 6 n
Success rate
from protein monomer to complexes
99% of all PDB XRC structures
New biological Insights
Statistical analysis of
PDB entries by end 2012
New Era for Structural Biology
XRC/NMR
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Complementarity of XPC, NMR and Cryo-TEM6/3/2018
NMR XPC EM
Towards an integrative structural biology approach!!
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Patwardhan, A. (2017). Acta Cryst. D73
Increasing numbers of high resolution structures
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Conformational insights: In-silico purification (still quite tricky…multi-body refinement)
6.6Å Eukaryotic Translational Initiation Complex.Low population of complex prevents (<3%) crystallization
Nakane (2018) BioXrv
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Why/How is cryoEM gaining so many adopters now?
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Ultrastable Microscopes: Autoloaders
31
• 24/7 operation without operator on site• Fully digital microscopy• Automated sample handling• Fully automated data collection (SPA and Tomography)• Easy-to-use
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Brilot, et al. 2012, JSB
Direct Detectors: super-resolution
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Technology Breakthrough Meets Market Demands
Added Value of Cryo-TEMDirect Electron Detection
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Why electrons?
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Serial Block Face Imaging
Tomography
Single Particle Analysis
Subramaniam 2005 Curr Opin Microbiol., modified TAW
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Electrons
• Involved in electricity, magnetism, thermal conductivity
• A moving electron creates a magnetic field
• Wave-particle duality
• Small particle • 9 x 10-28 grams
• Negatively charged • 1.6 x 10-19 Coulomb
• Higher wavelength • ~ 2 picometers @ 200 keV
• 90% the speed of light • 270,000 km/s
• Easily accelerated • resting energy 0.511 MeV
Williams & Carter, 1996
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TransmissionElectron
Microscopy (TEM)
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Transmission Electron Microscopy (TEM)
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F. deKok, 2012
Condenser Lenses (C1 – beam size,C2 –intensity)Condenser Aperture (reduces scattering)
Objective Lens (upper/lower pole piece)
Objective Aperture (contrast)
Projection Lens (3)
Fluorescent Screen
Digital Camera (CCD)
Filament (LaB6, FEG)
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Vacuum
• Electron microscopes have high vacuums…why?• Electrons are very easily scattered
• Want to control their trajectories
• Challenge for biological specimens• Most are hydrated (esp. proteins)
• How to work around?
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Vacuum: Pumps
Type Range (mbar) Use
Mechanical atm - 10-2 roughing, backing
Oil Diffusion 10-1 - 10-9 main, column
Turbomolecular 10-1 - 10-9 main, column
Ion 10-5 - 10-12 column, gun
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Filaments
Lanthanum Hexaboride Schottky Field Emitter
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Field Emission Gun: Types
LaB6
• JEOL JEM 1400
• Lanthanum Hexaboride
• Vacuum (10-4)
• Crossover = 10 micron
• $1K
W&C p.74
Schottky FEG
• FEI Tecnai F30 Twin
• Zirconium Oxide
• High Vacuum <10-6
• 0.015 micron
• $12K
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Spatial Coherence
• Perfect spatial coherence would be all electrons emit from the same point
• Smaller tips • more coherent• Better phase contrast• Better resolution
• Which tip has better spatial coherence?
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Field Emission Gun (FEG)
• Source of electrons = the “gun”
• Provides large stable current in a small electron beam
• Source determines resolution
• Tungsten (W) or ZrO2
W&C p. 80
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• FEG = cathode (-300 kV)
• Anode 1 = “extraction voltage”
• Positive by a few kV
• Intense electric field
• Electrons tunnel out
• Anode 2 = accelerates electrons
• TEM = 50-300 kV
Field Emission Gun: How does it work?
Produces a “refined” electrostatic lens for crossover
Produces electrons upon application of a large electric potential
W&C p.80
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Lenses:• Magnify or demagnify
• Illuminate
• Focus
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Lenses: what are they?
Electromagnets• Vary…
• current using a coil around a soft iron core
• Affects resultant magnetic fieldW&C p.97
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Lenses
W&C p.93
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Chromatic
Lens Abberations
Spherical
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Lens Abberations: Astigmatism
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Lens abberations: Astigmatism
Corrected
Astigmatism
Astigmatism
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Apertures
• Strip of metal
• 4 Holes drilled with decreasing size
• Limits undesirable scattering, leading to noise in images.
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Digital Camera
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Detective Quantum Efficiency
• Metric to compare efficiency of detection
• Where…• S = signal (electrons)
• N = Noise (background)
• A perfect detector would have a DQE of 1
• Detectors have <1
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Charge Coupled Device (CCD)
W&C p.120
• Metal-insulator-silicon devices that store charge
• Each pixel in an array • is an individual capacitor
• Isolated from each other
• Collect charge in the well
• Proportional to incident radiation intensity
• Our CCDs• JEOL = 2K x 2K
• F30 = 4K x 4K
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Renaissance in imaging…
• Direct electron Detection
• Revolutionizing cryo-EM
• Take movies and compensate for drift over course of acquisition
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Dose
• TEM is Electro-magnetic Radiation
• Damage to sample• “knock-on” – incoming electron interacts with atomic
nucleus
• Mass loss (decrease in sample thickness)
• Bubbling (hydrogen bonds broken)
• Limit doses given to sample• “Low Dose”
• 20-80 e-/Å2
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TEM Contrast mechanisms
Thickness Mass Diffraction
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Beam-specimen interactions
Elastic Scattering
• No Energy loss
• High angle (>5o)
• Interactions with nucleus or inner valence electrons
Inelastic Scattering
• Energy Loss
• Low angle <5o
• Interactions with outer valence electrons
• Lost energy as• X-rays• Plasmons• Beam damage• Heat/bubbling
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Reading/Watching• E. Callaway 2015 “Revolution will not be crystallized”
Nature News Feature
• A. Patwardhan 2017 Trends in the Electron Microscopy Data Bank (EMDB) Acta Cryst D
• Y. Cheng, et al. 2015 “A Primer to Single-Particle Cryo-Electron Microscopy” Cell
• A. Merk et al. 2016 “Breaking Cryo-EM Resolution Barriers to Facilitate Drug Discovery” Cell
• Grant Jensen’s CryoEM Videos 1&2
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Single Particle Reconstruction
• “quantitative way of determining the structure of macromolecules from micrographs, showing them as a collection of isolated, unattached particles”
• Uses not one, but thousands of macromolecules
• Multiple orientations or “Views” in 2D projections
• Group same views together, align and average
• Reconstruct 3D from multiple 2D views
Frank, 2009, QrevBiophys