slide set 15

Question 1

integrins what are they and what do they bind

Answer 1

membrane protein that binds the basal lamina

Question 2

integrins structure

Answer 2

dimer of alpha and beta subunits
24 types in human (8 beta, 18 alpha)
integrins bind extracellularly to ECM proteins and intracellularly to linker proteins that attach to actin

Question 3

important linker protein

Answer 3

talin!

Question 4

focal adhesions

Answer 4

clusters of multiple integrins bound to talin, linking to bundles of actin filaments (stress fibers)

Question 5

assembly

Answer 5

assembly and disassembly must occur in the right space at the right time for motility

Question 6

how do we study the role of focal adhesions in cell migration?

Answer 6

• fluorescently label a protein found in focal adhesions (EX: vinculin) and observe localization over time
• in video, cell moves with polarity

Question 7

ECM aka

Answer 7

extracellular matrix

Question 8

cells have to make and release attachments to ECM

Answer 8

• Outside-in signaling
  
  • integrin attachment to ECM triggers actin attachment on the inside
• Inside-out signaling
  
  • signals stimulate actin and associated proteins to associate with integrins
  • this changes conformation of the extracellular domain to bind ligand

Question 9

active vs inactive integrin

Answer 9

inactive (weak binding) state (folded)

active (strong binding state) (unfolded)

differences are due to changes in structure

used data from X-ray crystallography

Question 10

many integrins cluster together to form….

Answer 10

strong focal adhesions!

many other proteins cluster on the cytosolic side

(some bind to integrin tail, actin, or other proteins)

some of the proteins that make up a focal adhesion are enzymes that can detect tension generated by attachment to the ECM (more tension stabilizes the complex and forms larger adhesions

Question 11

FAK aka

Answer 11

focal adhesion kinase

Question 12

when is FAK active

Answer 12

FAK is active when cells are attached

Question 13

talin and mechanical sensing

Answer 13

talin contributes to mechanical sensing by integrin-based cell-matrix adhesions

tension causes talin to unfold partially and expose multiple sites to bind vinculin

vinculin binds actin filaments, which creates more tension and anchors for actin filaments

talin is a tension sensor

Question 14

Extracellular matrix (ECM)

Answer 14

cells synthesize and secrete the ECM and then organize it into a larger structure

Question 15

talin positive feedback loop

Answer 15

tension leads to binding leads to more tension

Question 16

ECM includes….

Answer 16

• bone, teeth
• tendon
• ligament
• cornea
• cartilage
• basal lamina
• connective tissues
• the proteins that make up the ECM provide strength and support, but also function in cell signaling (chemical and mechanical)

Question 17

3 broad categories of ECM proteins

Answer 17

proteoglycans and GAGs

fibrous proteins

glycoproteins

Question 18

basal lamina

Answer 18

thin layer of ECM that separates epithelial cells from the connective tissue

prevents fibroblasts from migrating into epithelial tissue, but immune cells can cross

cells on both sides secrete the proteins that make up the basal lamina

multiple components of ECM proteins are assembled to form it

components vary but most include laminin, type IV collagen, and sometimes fibronectin

Question 19

glycoproteins

Answer 19

laminin is the primary organizer of the basal lamina

other examples: nidogen, fibronectin

laminin anchors proteins to cells

image is electron micrographs of laminin molecules shadowed with platinum

Question 20

structural model of basal lamina attached to a cell’s integrins

Answer 20

Question 21

other type of glycoproteins in ECM

Answer 21

fibronectin, CYR61, tenascin, thrombospondin (don’t memorize)

many are large scaffold protein with multiple copies of specific protein-interaction domains

Question 22

proteoglycans

Answer 22

hyaluronan, perlecan, decorin, aggrecan

a protein core that is covalently attached to a sugar (specifically a glycosaminoglycan [GAG])

sugars provide hydration to tissues

the sugars are negatively charged, which attracts positively charged water molecules to form a hydrated gel

GAG sugars are not branched (unlike previous sugars we discussed)

Question 23

fibrous proteins

Answer 23

EX: type IV collagen, fibrillar collagen

collagens are major proteins of ECM

formed of 3 polypeptide chains, each called an alpha chain

alpha chains wrap around each other to form a stiff triple-stranded helix

Question 24

collagen molecules associate together into….

Answer 24

fibrils and fibers

Question 25

how do cells organize collagens

Answer 25

cells pull on collagens and organize them

2 pieces of chick embryo heart were cultured on a collagen gel

individual fibroblast cells migrate on the collagen, pulling on in and shaping it into fibers between the 2 pieces in the process

Question 26

ECM degradation

Answer 26

cells must degrade the ECM

ECM need to be degraded for normal turnover of proteins, remodeling of the ECM and for cells to migrate past it

extracellular proteases degrade ECM