Today’s Announcements Today’s take-home lessons(i.e. what you should be able to answer at end of lecture) • Read ECB: Will assign later today. • Homework assigned (later) today • Molecular motors: What are they? (3 families, 2 which walk on microtubules; one family which walks on actin) • Super-Accuracy: FIONA (nanometer accuracy, << l/2) • Confocal microscopy (Can discriminate according to z-axis) • Super-resolution microscopy—STED, STORM, (PALM next time) microscopy (gets resolution << l/2)
FIONA Fluorescence Imaging with One Nanometer Accuracy Very good accuracy: 1.5 nm, 1-500 msec
center width Diffraction limited spot: Single Molecule Sensitivity Accuracy of Center = width/ S-N = 250 nm / √104= 2.5 nm = ± 1.25nm Width of l/2 ≈250 nm Enough photons (signal to noise)…Center determined to ~1.3 nm Dye lasts 5-10x longer -- typically ~30 sec- 1 min. (up to 4 min) Start of high-accuracy single molecule microscopy Thompson, BJ, 2002; Yildiz, Science, 2003
Biomolecular Motors: Intra- & Extra-Cellular Motion • Characteristics • nm scale • Move along tracks • intracellular directional movement • cell shape changes & extracellular movement • Use ATP as energy source D K Actin, mtubules ATP-binding heads Nature Reviews ATP mechanical work Cargo binding Kinesin Myosin Dynein Motor Microtubule actinMicrotubule polymer
Streptavidin Quantum Dot Streptavidin conjugate Biotinylated Anti-Pentahis antibody Six-histidine tag Leucine zippered CENP-E dimer w/ six histidine-tag Axoneme or microtubule + - Motility of quantum-dot labeled Kinesin (CENP-E) 8.3 nm/step from optical trap
Kinesin (Center-of-Mass) Moving Kinesin moves with 8.4 nm /ATP step size.
Kinesin: Hand-over-hand or Inchworm? 8.3 nm 8.3 8.3 nm qs655 16.6 nm 16.6 nm 8.3 nm, 8.3 nm 16 nm 0 nm 16.6, 0, 16.6 nm, 0… [ATP] = 5 mM ; 4 msec exposure time (Originally 0.3 mM ; 500 msec exp. time) [ATP] (16.6x higher), 125x faster acq. pixel size is 160nm 2 x real time Toprak et al, PNAS, 2009
<step size> = 16.3 nm y ~ texp(-kt) 16 nm 16 nm 0 nm Takes 16 nm hand-over-hand steps (even at 5mM) Kinesin Can you derive this?
Kinesin: H-over-H, but how does neck not twist? Hand-over-hand: Head (foot) takes 16.6 nm steps 16 nm Inchworm: Head (foot) takes 8.3 nm steps Adapted from Hua, Chung, Gelles, Science, 2002 8 nm 8 nm Can you think of an experiment to figure this out?
Confocal Detection Sample is 3-D. Detectors are 2-D.How do you get z-axis sectioning with Microscopy?A pinhole allows only in-focus light through 3-D sample Detector (Intensity) Focused Light creates fluorescence which gets to detector Smaller the pinhole, better out-of-focus discrimination but lose more signal. Light mostly gets rejected Scan sample in x, y, z and reconstruct entire image
Confocal MicroscopyLots of different ways of arranging to get fast scanning: Moveable mirrors (only have to move sample in z-direction, Nipow disk….
3-D sectioning with Confocal Three-dimensional reconstruction of a series of 2D images of PMMA spheres
Can we achieve nanometer resolution? i.e. resolve two point objects separated by d << l/2? Super-resolution Breaking the classical diffraction limit Idea: 1) Make Point-Spread Function smaller << l/2 2) Make one temporally or permanently disappear, find center (via FIONA) and then reconstruct image.
STimulatedEmission Depletion (STED) S. Hell Sharpen the fluorescence focal spot is to selectively inhibit the fluorescence at its outer part. 200nm Net result is a smaller Point Spread Function http://www.mpibpc.gwdg.de/groups/hell/ Huang, Annu. Rev. Biochem, 2009
Biological Example of STED The transient receptor potential channel M5 Analysis of spot size for Confocal (A) and STED (B) images of TRPM5 immunofluorescence layer of the olfactory epithelium. (A, C Inset) Confocal image at a lower (higher; box) magnification taken with a confocal microscope. (B) STED image. Effective point-spread function in the confocal (189 nm) and STED (35 nm) imaging modes. Hell, PNAS, 2007
Basics of Most Super-Resolution MicroscopyInherently a single-molecule technique Huang, Annu. Rev. Biochem, 2009 STORM STochastic Optical Reconstruction Microscopy Bates, 2007 Science
Class evaluation 1. What was the most interesting thing you learned in class today? 2. What are you confused about? 3. Related to today’s subject, what would you like to know more about? 4. Any helpful comments. Answer, and turn in at the end of class.