Two heads are better than one: Single stranded DNA translocation of UvrD-family dimers vs. monomers

Two key strands of DNA research have converged in a new study, comparing the performance of single stranded DNA translocation by UvrD-family dimers and monomers. UvrD-family Superfamily 1A helicases are essential in various DNA processes including replication, recombination, repair, and transcription. Often, monomers need to be activated by dimerization to function as helicases in the absence of external forces or aids.

Mycobacterium tuberculosis UvrD1 helicase creates dimers through a disulfide bond between cysteines in the 2B sub-domains of each monomer, while E. coli UvrD employs a similar 2B domain interface to form non-covalent dimers.

Researchers explored an E. coli UvrD variant (R421C), which forms covalent dimers with inherent helicase activity. This provided an opportunity to compare ssDNA translocation and helicase activities of covalent dimers and monomers. The findings revealed that crosslinked UvrD dimers exhibit significantly higher ssDNA translocation processivities than monomers, despite similar translocation rates.

Furthermore, crosslinked UvrD dimers demonstrate highly processive DNA unwinding of thousands of base pairs, a capability far exceeding that of non-crosslinked UvrD dimers. Interestingly, monomers show no DNA unwinding activity. The rate of DNA unwinding in crosslinked UvrD dimers was only about 20% slower than their ssDNA translocation rates, suggesting they are 'active' helicases that directly aid in duplex destabilization.