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Paul R Selvin
| Contributions | 26 |
|---|---|
| Affiliation | University of Illinois, Urbana-Champaign |
| Web Site | http://www.physics.uiuc.edu/people/Selvin/ |
| Biography | Paul Selvin earned a Ph.D. from the University of California, Berkeley, in 1990. Formally it was in physics, but in reality, it was in biophysics. The last experiment for his thesis, for example, was measuring the torsional rigidity of DNA by looking at a fluorophore intercalated in DNA, twisting around. A paper based on this experiment was published in Science (Selvin, 1992, Science) and later confirmed in a single molecule experiment (Bryant, Nature, 2003). Professor Selvin did two sets of experiments during his postdoctoral training. One was developing a new type of fluorescence resonance energy transfer (FRET) based on lanthanides, called luminescence resonance energy transfer (LRET). He later used this technique to discover how a potassium ion channel, in part responsible for nerve conduction, responds to voltage (Cha, 1999, Nature; Posson, 2005, Nature). The second involved single molecule fluorescence—the first measurement of FRET between a single donor and single acceptor (Ha, 1996, PNAS). After joining the Department of Physics at the University of Illinois in 1997, his interest has turned to molecular motors—proteins whose job is moving cargoes around the cell. For example, chromosomes are bound to molecular motors (kinesin and dynein) and under their power, are moved into the two halves of a cell during cell division. Selvin’s task was to determine how the motors moved. They were known to be dimeric, with two “feet,” held together by a head that consumed ATP (the universal food of the cell) and a stalk that bound to the cargo. It was also known that for each ATP burned up, these proteins moved between 8 and 37 nm, depending on the individual motor. But did they move in a walking-type motion (also called “hand-over-hand”), or did they move as an inchworm does? A walking-type motion would move the back foot twice the center-of-mass distance, with the front foot not translating at all; an inchworm-type motion would move all parts equally—equal to the center of mass. The problem was that this distance for the walking motion was only 74 nm for the biggest motor, and 16 nm for the smallest motor—or 37 nm and 8 nm for an inchworm motion—about 30 times smaller than the diffraction limit of light, arguably the smallest distance that can be resolved with visible light. The trick to get around this problem was to realize that a single molecule’s position can be located arbitrarily well. It’s much like a mountain peak, which can be located to within a few yards, even though the mountain itself may be a a mile wide. Similarly, a single molecule’s center can be determined to be its width (~250 nm), divided by the square root of the numbers of photons collected (see left diagram). Selvin and his group managed to collect 10,000 photons in 0.5 s, meaning that the fluorophore’s center could be determined to ±1.25 nm (250/√104). With some clever chemistry, the single fluorophore could last several minutes, meaning that Selvin could watch the fluorescently-labeled molecular motor take several steps (Yildiz, 2003, Science). He called the technique FIONA—Fluorescence Imaging with One-Nanometer Accuracy. The first measurement was performed in vitro to control the amount of ATP that the motor “ate,” thereby slowing it down so each individual step could be seen. With FIONA, Selvin found that from the biggest motor, Myosin V, (Yildiz, 2003, Science) to the smallest motor, kinesin, (Yildiz, 2004, Science), to one in between (Myosin VI), (Yildiz, 2004, J.Biol.Chem.), the motors all moved in a hand-over-hand, or walking, fashion. This discovery won the award as one of the ten most significant advances in science for 2003, as judged by Science magazine. It also won for Selvin’s student, Ahmet Yildiz, Science’s grand prize (a world-wide competition) for the most noteworthy Ph.D thesis. Selvin then looked in vivo, i.e., inside a cell (Kural, 2005, Science). Here the time resolution had to be improved to 1 msec—a 500-fold increase—because the ATP was now not under his control, and was at a fairly high concentration. The motion of individual kinesins, and individual dyneins, could be measured, and surprisingly, they could move cargo around more than 10 times faster than what had been measured in vitro! Selvin is now combing FIONA with optical traps (holding particles with light) in vivo, to see how many motors are causing such large velocities. Selvin’s future plans call for measurements in situ, for example, in Planaria and in C. Elegans, to test how these motors act in “real life.” |
Contributions
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Lecture 10: Mutagenesis
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10 Apr. 2008 | Online Presentations | Contributor(s): Paul R Selvin
Site-Directed Mutagenesis to Isolate and Mutate DNA (for FIONA)
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Lecture 11: FIONA (Fluorescence Imaging with One Nanometer Accuracy)
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15 Apr. 2008 | Online Presentations | Contributor(s): Paul R Selvin
Fluorescence Imaging with One Nanometer Accuracy, Specificity to look at heads Nanometer spatial localization, Second temporal resolution, Single Molecule sensitivity Single Molecule Photostability
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Lecture 12: Ultra-Resolution
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15 Apr. 2008 | Online Presentations | Contributor(s): Paul R Selvin
SHREC (Single molecule High Resolution Co localization), SHRIMP (Super-High Resolution Imaging with Photobleaching), DOPI (Defocused Orientation Position Imaging), PALM (PhotoActivated Localization Microscopy), Enhancing Resolution
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Lecture 13: Fluorescence Resonance Energy Transfer (FRET)
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15 Apr. 2008 | Online Presentations | Contributor(s): Paul R Selvin
DNA Replication, FRET: measuring conformational changes of single biomolecules, Fluorescence Resonance Energy Transfer (FRET)
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Lecture 14: FRET and Helicase Activity
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15 Apr. 2008 | Online Presentations | Contributor(s): Paul R Selvin
FRET: measuring conformational changes of (single) biomolecules, Unzipping mystery of helicases
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Lecture 15: Confocal and STED Microscopy
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15 Apr. 2008 | Online Presentations | Contributor(s): Paul R Selvin
Confocal Detection, Energy Transfer, Confocal Microscopy, STED (Stimulated Emission Depletion),Improved resolution
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Lecture 16: Optical Traps - Part 1
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18 Apr. 2008 | Online Presentations | Contributor(s): Paul R Selvin
First Optical Trap built, Reflection, Refraction, Brownian motionYann Chemla
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Lecture 17: Diffusion - Part 1
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16 Apr. 2008 | Online Presentations | Contributor(s): Paul R Selvin
Diffusion, Directed motors, Thermal motion, nerve synapse, Efficiency of Diffusion
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Lecture 18: Magnetotaxis
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29 Apr. 2008 | Online Presentations | Contributor(s): Klaus Schulten, Paul R Selvin
Biochemical Mechanisms for Magnetic Orientation in Animals, guest lecture Klaus Schulten.
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Lecture 19: Optical Traps - Part2
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24 Apr. 2008 | Online Presentations | Contributor(s): Paul R Selvin
Biological application of optical traps, High resolution optical trapping, Brownian noise
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Lecture 1: Introduction to Biophysics
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29 Apr. 2008 | Online Presentations | Contributor(s): Paul R Selvin
Understanding biology using simple ideas from physics
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Lecture 20: Diffusion - Part2
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24 Apr. 2008 | Online Presentations | Contributor(s): Paul R Selvin
Diffusion and bacteria moving, power consumed by bacteria, Introduction to Reynolds number, Where Bacteria Live, How E. Coli move and swim,
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Lecture 21: Nerves
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25 Apr. 2008 | Online Presentations | Contributor(s): Paul R Selvin
Ion Channels,Ionic current, Gating current, Digital Ion Channels, Structural studies, X-ray Crystallography
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Lecture 22: Conformational Changes in Ion Channels
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25 Apr. 2008 | Online Presentations | Contributor(s): Paul R Selvin
Voltage dependence, Spontaneous shut-off, Nerve Impulse propagation, Structure Pore Domain, Voltage Sensor
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Lecture 23: Vision
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29 Apr. 2008 | Online Presentations | Contributor(s): Paul R Selvin
Summary of Ion Channels, Vision , Visual System, The Eye, Structure of the Eye, Signal Processing, Diffraction and Pupil
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Lecture 24: The 4 Molecules of life
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30 Apr. 2008 | Online Presentations | Contributor(s): Paul R Selvin
Atoms, Molecules, Macromolecules, you! Amino Acids, Sugars used as signals, Fatty Acids/Lipids
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Lecture 2: Central Dogma of Biology; Partition Function
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29 Apr. 2008 | Online Presentations | Contributor(s): Paul R Selvin
Nucleic Acids, DNA,RNA, Cell size, Nucleotides, Boltzman factor, Partition function
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Lecture 3: Nucleic Acids, RNA, and Proteins
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04 Mar. 2008 | Online Presentations | Contributor(s): Paul R Selvin
Nucleic Acids, Proteins, DNA Dimensions and Stability, How to make a nucleotide
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Lecture 4-1: Applications of DNA Technology: FISH, PCR, Forensics
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07 Apr. 2008 | Online Presentations | Contributor(s): Paul R Selvin
FISH (Florescence In Situ Hybridization), Gene Arrays("Chips") can be made
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Lecture 4-2: Applications of DNA Technology: FISH, PCR, Forensics
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07 Apr. 2008 | Online Presentations | Contributor(s): Paul R Selvin
DNA in the Cell , DNA Amplification with the Polymerase Chain Reaction (PCR), DNA Use in Forensic Paternity Cases, Sources of Biological Evidence, Short Tandem Repeats (STRs)
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Lecture 5: Magnetic Traps & DNA
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10 Apr. 2008 | Online Presentations | Contributor(s): Paul R Selvin
Introduction I
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Lecture 6: Magnetic Tweezers
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10 Apr. 2008 | Online Presentations | Contributor(s): Paul R Selvin
Introduction II and Applications
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Lecture 7: Single-Molecule of ATPase
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10 Apr. 2008 | Online Presentations | Contributor(s): Paul R Selvin
ATPase - How it produces ATP?
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Lecture 8: Resolutions
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10 Apr. 2008 | Online Presentations | Contributor(s): Paul R Selvin
X-ray diffraction (atomic resolution) Electron (Imaging) Microscopy (nm-scale) Visible (Imaging) Microscopy (nm - µm)
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Lecture 9: X-ray Structure and FIONA
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10 Apr. 2008 | Online Presentations | Contributor(s): Paul R Selvin
Accuracy vs. Resolution Measuring atomic distances Biomolecular Motors: Intra- AND Extra-Cellular Motion