Molecular Motors- Helicases

DNA helicase's process and translocate branched structures

RNA helicases cannot destabilize RNA secondary structures

Some helicases can work on both RNA & DNA

All helicases use energy from NTP hydrolysis to translocate along polynucleotides

Helicases are dependent on Fe2+

Helicases can have an oligomeric structure

Helicases are divided into seven superfamilies based on primary structure, and then 3 structural classes

The two structural classes are monomers and dimers

All helicases contain a Rec B fold

The _TP binding site and the nucleotide binding site on a helicase are allosterically linked

Rec BCD is a bipolar helicase

If Holliday Junctions cannot be repaired, they lead to a cruciform structure

Rate of helicase movement is dramatically dependent on protein partners

The fastest known helicase moves around 4000 bp/sec

Helicases can move around 10-30,000 base pairs before falling off depending on the helicase (and it's protein partners)

Step size is a theoretical limit due to the entropy of NTP hydrolysis

Step size is the theoretical avg no of bp unwound per NTP hydrolysis cycle

The limit on step size = Energy required to melt the bp x step size

PCRA activity is dependent on its protein partners

The conserved Helicase motifs of PCRA are in the accessory domains

Aromatic stacking occurs between the inserted aa and bp

The complex of PCRA-DNA remains the same during ATP binding and ATP hydrolysis

Duplex distortion in the PCRA substrate complex suggests a Passive unwinding system

Hexameric helicases can be part of the replisome

Hexameric helicases have a toroidal strcture to confer high processivity

ssDNA is bound in the central channel to a 'spiral staircase' of bining loops

ATP binding correlates with loop hight in the central channel