BIOL 4103 - Exam 3 Seibenhener Auburn University

NPF

Nucleation Promoting Factor

WH2 domain

Domain on NPF proteins in the WAVE family that

interact with profilin-bound ATP-actin

C and A

Domains on NPF proteins in the WAVE family that interact with ARP 2/3

WAVE

family of proteins that bind ARP 2/3 and Profilin-bound GTP-actin

Filamin

An actin-binding protein that cross-links actin filaments into networks.

Dimer of two subunits 280-kD each (560-kD total)

V-shaped molecule

Actin Binding Domain (ABD) is at the amino terminus and the Dimerization domain is at the carboxyl terminus.

Fimbrin

Bundles actin filaments with little space in between because this monomeric 68-kD protein is very small (14 nm)

Has 2 Actin Binding Domains (ABD)

Has 2 CA^2+ domains

ABD

Actin Binding Domain abbreviation

Filamin

Does Filamin or Fimbrin allow greater angles between actin filaments

Profilin

binds actin subunits and speeds elongation

Formin

nucleates assembly and remains associated with the growing plus end

Cofilin (aka ADF)

Breaks F-actin into smaller segments by destabilizing the filament, allowing for small amount of force to break the filament.

ADF

Actin Depolymerizing Factor abbreviation

Arp 2/3 (ARP complex)

Actin related protein complex which binds to the sides of existing filaments and nucleates the formation of branched actin networks

Tropomyosin

Protein that covers myosin binding sites on the actin molecules

crosslinked polymer

A polymer in which adjacent linear molecular chains are joined at various positions by covalent bonds.

Phalloidin

Drug that binds and stabilizes actin filaments.

Used with a fluorescent dye to visualize actin filaments in a cell

Fascin

Actin bundling protein that performs the same function that α actinin and fimbrin do

2 types of Actin bundles

parallel bundles and contractile bundles

parallel bundles

structure that contains closely spaced F actin aligned in parallel

functions to support outward projections from within the plasma membrane

FH2

Abbreviation for Formin Homology (domain) 2

Domain on each peptide in the Formin dimer that is wrapped around the barbed (+) end of the actin filament and adds ATP-Actin bound to profilin to the growing end of the F actin

FH1

Abbreviation for Formin Homology (domain) 1

Acts as a lasso to bring in Profilin-bound ATP-Actin for polymerization

Ena/VASP

protein that promotes actin's barbed-end polymerizing and inhibits capping protein binding

Persistant severing

severing of one actin filament into two by ADF/Cofilin. Event happens at low concentrations of ADF/Cofilin. The new filaments can either begin to grow again or degrade to G-ADP-actin to be recycled into G-ATP-actin by profilin for reuse

High cofilin concentration

possible outcomes resulting from cofilin binding:

breakage

bundling and rod formation

growth from barbed ends

Low cofilin concentration

possible outcomes resulting from cofilin binding:

persistant severing

degradation of new filaments

growth from barbed ends of new filaments

Myosin induced disassembly

results when myosin stays contracted very tightly over an extended period of time

Lamellipodia

Projection on the leading edge of the cell that propels the cell across the substratum

Branched actin filaments, so nucleation is reliant on Arp 2/3 complexes mostly

Crosslinking of these filaments is done by alpha-actinin and filamin

Filopodia

Projections extending beyond the leading edge of the cell thought to be involved in changes to cell direction

Unbranched actin filaments nucleating from formin mostly

Ena/Vasp proteins keep the actin bundles from being capped so they can grow indefinitely

Stress fibers and transverse arcs

Two types of contractile fibers

parallel to lamellipodia

Orientation of transverse arcs

perpendicular to lamellipodia

Orientation of stress fibers

stress fibers

Actin filaments concentrated into parallel bundles that function to pull the rear of the cell along during movement

Cell cortex

Reinforcing mesh of cytoskeletal elements under a plasma membrane

Contains both branched and unbranched actin filaments

Connected to the plasma membrane through ERM proteins

Invadopodia

Associated with metastatic tumor cells

Projection from the plasma membrane that allow the tumor cell to poke a hole and invade another cell

These are a way how cancer cells can metastasize into a host cell

Microtubules

Right handed helix made of tubulin protofilaments

Involved in organelle transport within a cell and cell division

Requirements for microfilament assembly

Calcium ion chelators

GTP

Tubulin

Colchicine

Depolymerizes tubulin microtubules by binding tubulin, inhibiting microtubule polymerization.

Colcemid

Depolymerizes tubulin microtubules by binding tubulin, inhibiting microtubule polymerization.

Chelator

Molecule that binds to a metal ion

GTP

Energy source required for microtubule assembly

Classical polymerization theory

Proposes that soluble tubulin begins to polymerize when it reaches a critical concentration in the cell, with the concentration of soluble tubulin staying constant when this occurs

Yes

Does treadmilling occur in microtubules?

Dynamic

Microtubulues are _______, always growing or shrinking at one end

Alpha tubulin

Tubulin subunit that binds GTP and has its GTP-binding site covered up by the binding of the other tubulin subunit

GTP is never hydrolyzed and provides structural support to the molecule

Beta tubulin

Tubulin subunit that binds GTP and has its GTP-binding site exposed to the surrounding environment

GTP can be hydrolyzed to GDP in this subunit

This subunit's bound guanine phosphate must be in the GTP state for tubulin polymerization to occur.

Dimerization of tubulin

First step of microfilament assembly

Oligomer

Short chain of monomers that is not long enough to be considered a polymer.

Heterodimer

The alpha and beta tubulin subunits dimerize to form tubulin that is a ___________

Protofilament

linear chain of tubulin subunits about 15-16 units long

GTP

What is the beta tubulin subunit bound to at the plus (+) end of the protofilament/microtubule?

GDP

What is the beta tubulin subunit bound to at the minus (-) end of the protofilament/microtubule?

13

How many protofilaments assemble laterally to form a microtubule?

Left handed

Handedness of the microfilament helix

Inter-PF contacts

Lateral contact sites between protofilaments in a microtubulule. Almost all of these contacts are homologous (beta-beta or alpha-alpha) except at the seam, where the contacts are heterogenous (alpha-beta)

Intra-PF contacts

Contact sites between tubulin subunits of a protofilament

PF

Abbreviation for protofilament

Seam

Only place where heterogenous inter-protofilament contact sites are

How colchicine and colcemid are used to treat cancer

Colchicine and colcemid bind tubulin, inhibiting microtubule polymerization, which in turn blocks mitosis

Disassembly

Which is faster, assembly or disassembly?

Dynamic instability

Co-existence of growing and shrinking microtubules in the same conditions

GTP hydrolysis on beta tubulin

A curved microtubule is a sign of a weak microtubule and is caused by what?

GTP cap

Band of GTP bound to beta tubulin at the plus end of a microtubule

Rescue

The transition from microtubule shrinkage to growth

CLASP

Proteins that mediate rescue

Catastrophe

Transition from growth to shrinkage

Occurs when rate of GTP hydrolysis is faster than the rate of GTP-tubulin assembly

GTP islands

Regions of GTP-bound beta tubulin on a protofilament that can spontaneously initiate rescue

Spastin and fidgetin

Enzymes other than katanin that function to break the microtubule

Katanin

Severs microtubules like a katana severing a paper towel roll

suuh veeeer innnnggg

How to pronounce the word "servering" according to our prof

MTOC

Abbreviation for Microtubule Organizing Center

MTOC

Structure from which microtubules grow

Centrosome

Made of two perpendicular centrioles and the pericentriolar material

Gamma tubulin

Type of tubulin that, along with associated proteins, forms a ring complex from which microtubules are nucleated within cells

Alpha tubulin

Which subunit of the tubulin heterodimer attaches to gamma tubulin?

Juxtanuclear

means "next to the nucleus"

pericentriolar material

Surrounds the centrioles and contains hundreds of ring-shaped complexes composed of the protein gamma tubulin

The complexes involving gamma tubulin are the organizing centers for the growth of the mitotic spindle.

GCP2 and 3

Tubulin gamma complex proteins

Connect gamma tubulin and SPC110

Spc110

Spindle pole complex protein 110

subunit of the gamma tubulin small complex

gamma-TuSC

Gamma Tubulin Small Complex

gamma-TuRC

Gamma Tubulin Ring Complex

gamma-TuRC

Ring complex of gamma-TuSC proteins

Where microtubule nucleation begins

Located in the MTOC

gamma-TuSC

Protein complex where nucleation of a protofilament occurs

Located in the MTOC

Augmin

Complex that allows microtubules to branch at 40 degrees from existing microtubules

Is responsible for non-MTOC gamma-TuRC localization (so that nucleation can occur)

MAP

Abbreviation for Microtubule Associating Proteins

MAPs

Proteins that interact with the microtubules of the cellular cytoskeleton

Class 1 MAPs

MAPs that promote the assembly of microtubules, or prevent the dissociation of microtubules

e.g. Tau, MAP1, MAP2, MAP4

Class 2 MAPs

MAPs that destabilize microtubules

e.g. MCAK, EB1, Kinesin 8/13

Type 1 and type 2

two types of class 1 MAPs

Type 1 MAP

Prevent microtubule dissociation by binding class 2 MAPS like EB1/3 and thus reduce the effective concentration of EB1/3 available to bind to microtubules enhancing microtubule polymerization

Do not actually bind to the microtubule itself

e.g. MAP1a and MAP1b

Type 2 MAP

MAPs that bind to the microtubule itself, providing stability, promoting rescue, or preventing depolymerization

e.g. MAP2 and MAP4

Tau protein

MAP that normally functions to hold protofilaments together when it is dephosphorylated

Hyperphosphorylation

Reaction that leads to dissociation of tau from the microtubule and development of paired-helical filaments

Tau hypothesis

Hypothesis that states that excessive or abnormal phosphorylation of tau results in the transformation of normal adult tau into PHF-tau and NFTs

PHF-tau

Abbreviation for Paired Helical Filaments of Tau

NFT

Abbreviation for Neurofibrillary Tangles

+TIPS

Abbreviation for + end Tracking Proteins

+TIPS

Proteins that follow the + end of a microtubule wherever it goes, proteins of all function do this

Hitchhiking

Attaching to a motor protein to get to the + end of a microtubule

cross-linking proteins

What in a cilium/flagellum causes the microtubules to bend, not just slide?

Axoneme

core of cilia that is the structural basis for ciliary movement