Actin

1
Actin
Highly conserved Most abundant
intracellular protein (in eukaryotes)
Fig 18-4
2
Structure of actin
Polarity of molecule - and ends T form
and D form G- actin vs F- actin
Fig 18-2
3
Structure of actin
View from -end
Fig 18-2
4
Bundles and Networks
What is the benefit of these kinds of
associations?
5
Stability of actin
Stability depends on environment ion and g-actin
concentration Provides support
through DYNAMIC arrangements including both
structure and gel-like qualities of cytosol
6
Actin filaments dynamics
Filaments utilizes 3 steps lag period,
elongation, steady state ATP hydrolysis NOT
required for polymerization ATP hydrolysis
changes kinetics of polymerization
vs - end?
http//www.bms.ed.ac.uk/research/smaciver/lectures
/Cs2.htm
Illustration of treadmilling CBI 25.2
7
Microtubules
Protofilament Polymer of a /b tubulin
heterodimers 13 protofilaments microtubule
Stable and unstable populations Exhibit dynamic
instability
Fig 19-5
Fig 19-1
8
Microtubule dynamics
http//www.bms.ed.ac.uk/research/smaciver/lectures
/Cs2.htm
vs - end
Steps in formation protofilament
formation microtubule assembly microtubule
elongation
Microtubules treadmill AND undergo dynamic
instability
9
Factors effecting polymerization/ depolymerization
Critical Concentration Cc Actin ends have
different Cc () 0.1mM (-)
0.8mM cellular concentration 0.5mM Consequences
? Microtubules One end in
MTOC Consequences? Associated proteins Toxins
10
And why are we discussing this?
Shmoos form from reorganization of actin
cytoskeleton Shmoo tip extends due to vesicles
specifically delivered via actin bound motor
protein Microtubules are main highway
vesicular traffic
11
Why important for neuronal function?
Fig 23-30
Actin in development CBI21.5 Microtubules in
axon core and protein localization Intermediate
filaments in mechanical stability of neurons
12
What makes one MT different from another?
Accessories!
13
Regulating Effective Concentrations
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Toxins
Effecting Actin Cytocholasin D Latrunculin Phal
loidin
Bind ends Bind G-actin Bind between subunits on
F-actin
Effecting Microtubules Colchicine Colcemid Ta
xol Vinblastine
Block formation by binding MT end (favors
depolymerization) Same as colchicine but
reversible Stabilizes by binding sides Lo
concentrations act like taxol hi promotes
crystalline arrays
Net effect on cell-- death Research and
Medicinal purposes for some
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Associated proteins cellular
Roles of associated proteins
16
Could this relate to Bipolar Disorder?
http//cellbio.utmb.edu/cellbio/microtubule_struct
ure.htmMAPs
17
Next time
Introduction to molecular motors