Regulation and activation of UvrD-family DNA helicases/ translocases.

For the past few decades, the active form of superfamily 1A (SF1A) UvrDfamily helicases has been controversial due to the absence of structures of the active dimeric form of these enzymes.

A key interaction in the monomeric structures is between a regulatory domain (2B) and duplex DNA that was proposed to facilitate DNA unwinding but is likely inhibitory.

However, recent cryo-EM structures show that Mycobacterium tuberculosis UvrD1 forms a covalent dimer, with dimerization occurring between the 2B domains of each subunit, resulting in major reorientations of the 2B domains that prevent the 2B–DNA interaction, thus relieving its inhibitory effect.

The same dimerization interface is used in Escherichia coli UvrD dimers, suggesting that this is a general mechanism to activate most SF1A helicases.

Due to these insights, textbook descriptions of helicase mechanisms based on the monomeric structures require re-evaluation. sciencenewshighlights ScienceMission https://sciencemission.com/conundrum-resolved

Superfamily 1 helicases are conserved nonhexameric ATP-dependent enzymes that unwind DNA and RNA duplexes processively or remove proteins, playing critical roles in DNA repair, replication, recombination, and RNA processing. While crystal structures of Superfamily 1A UvrD-family helicases suggested that monomers are active helicases requiring an essential 2B regulatory domain–DNA interaction, biochemical studies show that helicase activation requires dimerization. Recent cryo-electron microscopy (EM) structures of Mycobacterium tuberculosis UvrD1 dimers reveal that dimerization involves the 2B domains, eliminating their inhibitory interaction with duplex DNA, contradicting these original models. Escherichia coli UvrD dimers use the same dimerization interface, suggesting a general mechanism for this class of helicases.