lecture 2 what do we do? (projects in the sukharev lab)
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Lecture 2 What do we do? (projects in the Sukharev Lab). Reading for the next classes: Chapter 2 (Chemical foundations). What is the wavelength if the. frequency of atomic oscillations f = 10 14 s -1. c = f ∙ l. c = 3 ∙ 10 8 m/s (in vacuum). l = c/ f = 3 ∙ 10 -6 m = 3 m m. - PowerPoint PPT PresentationTRANSCRIPT
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Lecture 2
What do we do? (projects in the Sukharev Lab)
Reading for the next classes: Chapter 2 (Chemical foundations)
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frequency of atomic oscillations f = 1014 s-1
What is the wavelength if the
c = f ∙
= c/ f = 3 ∙ 10-6 m = 3 m
c = 3 ∙108 m/s (in vacuum)
infrared
470 nm = blue 530 nm = green600 nm = yellow 650 nm = orange700 nm = red >800 nm = infrared
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wavenumber = 1/
The stiffer is the bond the higher is frequency and smaller wavelengthIt also depends on the mass of the atom
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Basic Senses
• Vision
• Taste
• Smell
• Hearing, Equilibrium and Touch
• Temperature sensation
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Mechanical forces in the body
Force detectionFaint sound ~10-4 N/m2
Systolic pressure ~104 N/m2
Postural pressure on an intervertebral disk ~105 N/m2
Osmotic pressure (0.1M sugar gradient) = 2.4x105 N/m2
- It can’t be one receptor!!!
Force generationMolecular motors? Yes, but what exactly drives the tissue boundary formation and organogenesis in development: how do the feedback loops work?
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These are cartoons of the gating process. There is no structural information about any of the eukaryotic channels. However, such information is available for two prokaryotic channels, MscL and MscS
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?
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Bacterial osmoregulation
Osmoticallybalanced medium
Low osmolaritymedium
Open MS channels
(γ = tension)
HH22OO
HH22OO
ππOSMOSM
γγ
γγ
Prevent lysis
After Britten & McClure, 1962
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MscS MscL
MscK
Patch-clamp recording of channels with a glass pipette
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Tb MscL (Chang et al. 1998)
Eco MscS (Bass et al., 2002)
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The gating mechanism of MscL (E. coli model)
H.R Guy
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Lipids can be distorted near the edge of the flattened protein (due to the thickness mismatch), but their elastic recoil may help closing the channel.
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Two-State Model
A Boltzmann equation for the ratio of open and closed state probabilities, it dictates the dose-response relationship, i.e. fraction of open channels versus tension (gamma).
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Amodel = 23 nm2
18 nm2 ~41 nm2
Aexp = 20 nm2
Pore diameter predicted from conductance ~ 2.9 nm
Modeled expansion of MscL well corresponds to experimental data
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F7C-F7C
F10C-F10C
I24C-G26C
I32C-N81C
L121C-L122C
L128C-L129C
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L121C-L122C
L128C-L129C
I32C-N81CA20C-L36C
I3C-I96C
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The Crystal Structure of MscS (286 aa)
from Bass et al., Science, 298(2002)1582
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Bass et al, 2002
The kink region in MscS (electron densities)
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MscS-like channels are found in most organisms with walled cells
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From Haswell and Meyerowitz, 2006
Mutations in the Arabidopsis msl2 and msl3 genes lead to swelling and improper division of plastids
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Cross-section of the transmembrane domain and gate regions of MscS
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MscS constriction is largely dehydrated based on Molecular Dynamics simulations
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Gating by ‘bubble’ implies capillary evaporation in the hydrophobic confinement
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Hydrophilic substitutions favor pore wetting in simulations and strongly influence the speed of transitions in experiments
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C1
C2
C3/O*
O4
WT (2-state)E 23.4 kT 24 kTA 22.8 nm2 17.7 nm2
A98SE 12.1 kT 14.0 kTA 13.7 nm2 13.5 nm2
Energies and expansion areas from 4-state analysis
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Key stages in model development
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Transitions between the functional states reveal distinct conformations of the pore lining TM3 helices
Alternate Kink at G121Kink at G113
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Double alanine mutant traps the open state
•G113A/G121A
•High helical propensity at both G113 and G121 kinetically traps MscS in the open state
WT
G121AG113A
G113A/G121A
Straight TM3 helices are a feature of the open
state
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Separation of peripheral helices
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F68S mutant is prone to fast and silent inactivation