Hitchcock-Degregori - Cytoskeleton II (motors)

Question 1

Classes of cytoskeletal motors (3)

Answer 1

1) Myosins: move on actin
2) Dyneins: move on microtubules from +–>-, periphery–>center
3) Kinesins: move on microtubules from —>+, center–>periphery
- all are ATPases, use ATP hydrolysis for conformational change + mechanical work, have multiple isoforms
- vesicle movement uses multiple motors (since they go both ways)

Question 2

Myosin

Answer 2

Actin motor. 2 heavy chains and 2+ light chains, 2 heads contain ATPases, tail binds target like vesicle so “unique identifier” of subclass. Most myosins move toward + end of actin.

Question 3

Kinesin

Answer 3

Like mysosin, head domain contains ATPase. C or N terminus in neck domain determines - or + activity. Stalk allows dimerization, tail binds target

Question 4

Dynein

Answer 4

Huge (2mil+daltons). Retrograde movement, 6 subunits, tail binds target. Part of AAA proteins (ATPase Associated with diverse cellular Activities).

Question 5

Primary Ciliary Dyskinesia (PCD, Kartagener’s Syndrome)

Answer 5

Causes respiratory tract infection, male infertility due to dynein mislocalization preventing ciliary activity. Mutation is in dynein heavy chain of outer microtubules (in 9+2, normally see dynein associated with 9, small lumps. Lacking in PCD)
-associated with situs inversus

Question 6

Myosin Mechanism

Answer 6

Myosin attached to actin. ATP binding allows dissociation from actin, movement to new site. ATP hydrolysis, rebind actin weakly. Dissociation from Pi is required to rebind actin strongly and contract (rate limiting step). So myosin ATPase determines activity and speed.

Question 7

Omecamtiv mecarbil (OM)

Answer 7

Treats acute cardiac failure. Binds cardiac myosin II, increases rate of Pi dissociation and therein contractility

Question 8

Kinesin mechanism

Answer 8

Similar to myosin. Leading head is associated with myosin, lagging head is ADP-bound and floating. Lead binds ATP, hydrolyzes. Lagging moves up, binds myosin, dissociates from ADP. Pi dissociates from new lagging (former lead), weakening its binding. Repeat.

Question 9

Dynactin: ex of motor protein tail specificity

Answer 9

Binds to dynein tail, vesicular cargo and microtubule. Complex includes spectrin. Increases functionality of dynein, allowing microtubule binding.

Question 10

Melanosomes: ex of vesicular delivery on microtubules

Answer 10

Myosin Va transports melanosomes on actin, with melanophilin and Rab27aGTP intermediating. RabGTPs key for sending myosins to specific membranes. Mutations in any of these components causes dysfunctional transport.

Question 11

Griscelli Type I and Elejalde Syndromes

Answer 11

Caused by melanophilin/Rab27aGTP mutations. Prevent melanosomes from moving from basal–>cell periphery, causing silver-hair light-skinned babies from dark-skin parents. Neurological disorders.

Question 12

Actin-myosin contraction

Answer 12

Polymerization drives cell migration through myosin contraction, also cytokinesis (and neural tube development through similar mechanism)