8. Roles of Actin Filament Remodeling in various cellular process
CytokinesisCell Motility
PhagocytosisVesicle Transport
Asymmetric spindle Positioning in Oocyte
9. Actin Filament is dynamic
Formation of Actin filaments
• When?
• How long?
• Where?
• How looks like?
11. Actin Nucleators Determine type of Filament Structure
Arp2/3 complex
:59 Annual Reviews AR131-19
REGULATION OF ACTIN FILAMENT NETWORK 651
ure 1 Electron micrographs of branched actin filaments. (a) Electron micrograph of
leading edge of a migrating Xenopus keratocyte prepared by detergent extraction and
ry shadowing. (b) Detail of boxed region from (a), with a branched filament network
ed in blue. (c) Gold-labeled antibody to ARPC2 localized to a branch point in the
ment network at the leading edge. (d ) Branch formed in vitro by pure actin filaments
Acanthamoeba Arp2/3 complex. (a–c) modified from 14. (d ) Modified from 13.
p2/3 complex (hereafter referred to as nucleation promoting factors), are being
Formins
Straight actin bundles
In Stress fibers and
filopodia
Branched actin filaments
in Lamellipodia
Spire
Straight Fiber
Oocyte development
Vesicle Transport
12. Arp2/3 complex:
6 Protein complex makes branched networks
Arp2
Arp3
ARPC3ARPC1
ARPC5
ARPC4
ARPC2
Dominguez and Namgoong, Comphrensive Biophysics 2012
Arp2
Arp3
ARPC3ARPC1
ARPC5
ARPC4
ARPC2mother filament
barbed end
barbedend
Nucleation Promoting Factor (NPF)
13. 18 85 161 200 245 436 498
N-WASP Pro-rich
26 136 200 270 400 501
WH1 GBDB AW CW
WAVE2 Pro-richhelix B AW C
JMY MA spectrin-like AW CW WPro-rich
40 300 620 790 855 983
profilin-actinregulation/localization
Prototypical NPF AW CWWPro-rich
actin Arp2/3
167 202 290 303 360 465
WASH
Pro-richWHD1 AW CWHD2
Arp2/3 complex WCA + actin transition complex activated complex
+
branch
70º
2
4
5
1
Arp2
Arp3
3
Nucleation Promoting Factor (NPF) are essential for
Arp2/3 mediated filament nucleations
14. Formins
Rho actin
Pro-rich (FH1) FH2CCDD DADDIDGBD
73 130 377 452 570 736 1175 1200
autoinhibition
profilin-actin
DD
DID
DAD
Complex of DID and DAD
DID
GTP-Rho
DD
GBD
Binding of Rho GTPase
linker
lasso
knobcoiled coil
post
FH2 Domain
3
1
4
21
2 4
barbed end
barbed end
3
1
4
2
1
2 4
3
• Responsible for the straight bundles of filaments (Stress fiber,
Fillopodia)
• 15 formins (8 subclass) in human and mouse
• Caps fast growing ends (barbed end) of actin filament and enhance
elongation rates
• Regulated by autoinhibition and small GTPase (Rho)
16. 1253
1128
158 445 507
Sra1
Nap1
90 172 202 498 559
W C Ahelix
meander
Pro-rich region
WAVE1
Abi2
75
HSPC300
L697
Y704
L841
F844
W845E434 F626 M632R190C179
basic
Rac1-binding
SH3
Nap1
HSPC300
Sra1
Abi2
WAVE1
WAVE1 Polybasic region
(proposed membrane-binding site)
proposed Rac1-binding site
W
C
C-terminal part polybasic region and Pro-rich sequence of WAVE1
substituted by a short linker (disordered in structure)
Pro-rich region and SH3 domain
removed for crystallization
disordered
18. Actin Capping Proteins
- Barbed End (Fast-Growing End) Capper
CapZ : Stop Elongation of Actin Filaments
- Pointed End Capper
Tropomodulin : Protect Actin filaments from Depolymerization
19. Capping Proteins : inhibit elongation and stabilize
actin filaments
CapZαβ : Capping fast growing (Barbed) end
Gelsolin : Severing and Capping Proteins
26. Myosin walk on actin filaments
- Except Myosin VI, every myosin move from
Slow growing end (pointed end)
- Hydrolysis of ATP provides energy for the movement
29. Actin filaments in Lamellipodia is mainly formed as branched filaments by
Arp2/3 complex
Actin filaments in Fillopodia is mainly formed as straight bundle by Formins
and Arp2/3 complex
33. Asymmetric division
Actin Cap
4N
GV GVBD
Spindle
Formations
Spindle
Migration
MII
Arrest
2N
2N
1N
1N
Fertilization
Polar Body
Adapted from Yi and RI, Cytoskeleton (2012)
34. Actin Nucleators in Asymmetric Spindle
Migrations
Gene Phenotype Method Referenc
es
Formin
(FMN2)
Failure of Spindle
Migration
Symmetric division
Knockout mouse
fmn2 (-/-)
Spire Failture of Spindle
Migration
Failure in Cytokinesis
siRNA
knockdown
How about Arp2/3 and Nucleation Promoting Factors?