Intro to Motors and Helicases Flashcards
What is processivity?
The average distance travelled before a motor falls off the track
What unit is used to measure processivity?
Distance/binding event
What is units is step size measured in?
Distance per ATP hydrolysis
What is motor-coupling efficiency?
How many ATPs are used to make a successful step
What units are used for motor-coupling efficicency?
ATPs per step
What is polarity in relation to Motors?
The tracks are asymmetrical and have a positive and negatie end
What is the general structure for a P-loop?
Central beta sheet surrounded by alpha-helices
What is the function of the P-loop?
It cradles the triphosphate tail of ATP
What metal ion is required in motor proteins and helicases?
Mg2+
What are the 3 motifs found in helicases?
- P-loop
- Walker A
- Walker B
Why is Mg2+ needed as a cofactor in helicases?
Co-ordinates the beta and gamma phophates of ATP which is important for hydrolysis
Why is the walker B motif important?
- It co-ordinates Mg2+
- Often contains a catalytic residue that acts as a base to activate a water molecule to cause ATP hydrolysis
What is a helicase?
An enzyme which couples ATP hydrolysis to the unwinding of DNA (separation of duplex DNA into single strands)
What is the typical processivity of helicases?
50,000 bp
How many ATP are required for 1 step of helicases?
1 ATP
What is the step size of helicases?
1 base pair
What is the polarity of helicases?
Either 3’ to 5’ or 5’ to 3’
What do helicases require to get going on the DNA?
- Overhangs
- Loading factors
What is a classical helicase?
A protein which produces ssDNA in biochemical assays
Which 3 motifs do all helicases contain?
- Walker A
- Walker B
- Arginine finger
What processes are helicases involved in?
- DNA replication
- DNA repair and recombination
- Transcription regulation
- Import/export of DNA/RNA
What do translocases do?
Many translocases contain helicase motifs but do not possess classical strand separation
How can helicases manipulate DNA besides just unwinding?
- Remodel DNA by remodelling holiday junctions
- Act as a mechanism of moving another enzyme along DNA
- Displace or move other proteins along/off DNA
What are ‘non-classical’ helicases?
Proteins which are found to have shared helicase sequence motifs and which move along DNA but which do not necessarily unwind it
