Helicase Structural Classification

Question 1

How many superfamilies of helicases are there?

Answer 1

6

Question 2

Do all members of the 6 helicase superfamilies contain P loop folds?

Answer 2

Yes

Question 3

How many core domains do helicase superfamilies 1 and 2 contain?

Answer 3

2

Question 4

How many core domains do helicase superfamiles 3-6 contain?

Answer 4

1

Question 5

What direction does PcrA helicase move?

Answer 5

3’ to 5’

Question 6

What functions does PcrA helicase undergo?

Answer 6

• Multifunctional DNA repair factor
• Nucleotide exision repair
• Mismatch repair

Question 7

Which domains play important roles in binding the DNA duplex in PcrA helicase?

Answer 7

1B and 2B

Question 8

How does PcrA helicase unwind the DNA?

Answer 8

• 3’ end extends across both core domains forming a motor
• Motor walks along ssDNA, pulling it into a enzyme and displacing the other strand across 2A domain

Question 9

Where does binding and hydrolysis of ATP occur in PcrA helicase?

Answer 9

Between core domains

Question 10

What are the helicase core domains?

Answer 10

tandem RecA-fold

Question 11

Where does ssDNA bind in PcrA helicase?

Answer 11

In aromatic pockets across the top surface of core domains

Question 12

What helicase superfamily is PcrA helicase a member of?

Answer 12

SF1

Question 13

What is the structure of SF3 hexameric helicases?

Answer 13

• 6 repeats of p-loop folds
• Single core domain

Question 14

Where does ssDNA bind in SF3 hexameric helicase?

Answer 14

Within the centre

Question 16

Where does ATP bind in SF3 hexameric helicases?

Answer 16

At the interface of each RecA fold

Question 17

How does the arginine finger interact with ATP in SF3 Hexameric Helicases?

Answer 17

It interacts with the ATP on the neighbouring subunit

Question 18

Though there are 6 sequence classes of helicases how many major structural classes are there and what are they?

Answer 18

• 2 major classes
• Superfamily 1 and 2
• Superfamily 3 to 6

Question 19

How does a ring structure allow helicase to unwind DNA?

Answer 19

The ring structure acts as a mechanical wedge, stripping the strands apart

Question 20

What is a problem with the ring helicase method of separating DNA?

Answer 20

How do you prevent immediate reannealing of the strands?

Question 21

How do you prevent immediate reannealing of the DNA strands once they have been separated by a helicase?

Answer 21

Accessory proteins may separate strands and prevent reannealing

Question 22

What mechanism do helicases use for enery transduction?

Answer 22

RecA/AAA+ folds

Question 23

Are RecA/AAA+ folds used in tandem or distinct subunits?

Answer 23

Can be either tandem or distinct